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Remove the "snapshot too old" feature. 

Remove the old_snapshot_threshold setting and mechanism for producing
the error "snapshot too old", originally added by commit 848ef42b.
Unfortunately it had a number of known problems in terms of correctness
and performance, mostly reported by Andres in the course of his work on
snapshot scalability.  We agreed to remove it, after a long period
without an active plan to fix it.

This is certainly a desirable feature, and someone might propose a new
or improved implementation in the future.

Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CACG%3DezYV%2BEvO135fLRdVn-ZusfVsTY6cH1OZqWtezuEYH6ciQA%40mail.gmail.com
Discussion: https://postgr.es/m/20200401064008.qob7bfnnbu4w5cw4%40alap3.anarazel.de
Discussion: https://postgr.es/m/CA%2BTgmoY%3Daqf0zjTD%2B3dUWYkgMiNDegDLFjo%2B6ze%3DWtpik%2B3XqA%40mail.gmail.com
This commit is contained in:
Thomas Munro 2023-09-05 18:26:12 +12:00
parent aa0d350456
commit f691f5b80a
50 changed files with 21 additions and 1425 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
contrib/Makefile
View File

@ -29,7 +29,6 @@ SUBDIRS = \
lo \
ltree \
oid2name \
old_snapshot \
pageinspect \
passwordcheck \
pg_buffercache \

1
contrib/bloom/blscan.c
View File

@ -132,7 +132,6 @@ blgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
if (!PageIsNew(page) && !BloomPageIsDeleted(page))
{

1
contrib/meson.build
View File

@ -37,7 +37,6 @@ subdir('lo')
subdir('ltree')
subdir('ltree_plpython')
subdir('oid2name')
subdir('old_snapshot')
subdir('pageinspect')
subdir('passwordcheck')
subdir('pg_buffercache')

21
contrib/old_snapshot/Makefile
View File

@ -1,21 +0,0 @@
# contrib/old_snapshot/Makefile
MODULE_big = old_snapshot
OBJS = \
$(WIN32RES) \
time_mapping.o
EXTENSION = old_snapshot
DATA = old_snapshot--1.0.sql
PGFILEDESC = "old_snapshot - utilities in support of old_snapshot_threshold"
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/old_snapshot
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

23
contrib/old_snapshot/meson.build
View File

@ -1,23 +0,0 @@
# Copyright (c) 2022-2023, PostgreSQL Global Development Group
old_snapshot_sources = files(
'time_mapping.c',
)
if host_system == 'windows'
old_snapshot_sources += rc_lib_gen.process(win32ver_rc, extra_args: [
'--NAME', 'old_snapshot',
'--FILEDESC', 'old_snapshot - utilities in support of old_snapshot_threshold',])
endif
old_snapshot = shared_module('old_snapshot',
old_snapshot_sources,
kwargs: contrib_mod_args,
)
contrib_targets += old_snapshot
install_data(
'old_snapshot.control',
'old_snapshot--1.0.sql',
kwargs: contrib_data_args,
)

14
contrib/old_snapshot/old_snapshot--1.0.sql
View File

@ -1,14 +0,0 @@
/* contrib/old_snapshot/old_snapshot--1.0.sql */
-- complain if script is sourced in psql, rather than via CREATE EXTENSION
\echo Use "CREATE EXTENSION old_snapshot" to load this file. \quit
-- Show visibility map and page-level visibility information for each block.
CREATE FUNCTION pg_old_snapshot_time_mapping(array_offset OUT int4,
end_timestamp OUT timestamptz,
newest_xmin OUT xid)
RETURNS SETOF record
AS 'MODULE_PATHNAME', 'pg_old_snapshot_time_mapping'
LANGUAGE C STRICT;
-- XXX. Do we want REVOKE commands here?

5
contrib/old_snapshot/old_snapshot.control
View File

@ -1,5 +0,0 @@
# old_snapshot extension
comment = 'utilities in support of old_snapshot_threshold'
default_version = '1.0'
module_pathname = '$libdir/old_snapshot'
relocatable = true

142
contrib/old_snapshot/time_mapping.c
View File

@ -1,142 +0,0 @@
/*-------------------------------------------------------------------------
*
* time_mapping.c
* time to XID mapping information
*
* Copyright (c) 2020-2023, PostgreSQL Global Development Group
*
* contrib/old_snapshot/time_mapping.c
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "funcapi.h"
#include "storage/lwlock.h"
#include "utils/old_snapshot.h"
#include "utils/snapmgr.h"
#include "utils/timestamp.h"
/*
* Backend-private copy of the information from oldSnapshotControl which relates
* to the time to XID mapping, plus an index so that we can iterate.
*
* Note that the length of the xid_by_minute array is given by
* OLD_SNAPSHOT_TIME_MAP_ENTRIES (which is not a compile-time constant).
*/
typedef struct
{
int current_index;
int head_offset;
TimestampTz head_timestamp;
int count_used;
TransactionId xid_by_minute[FLEXIBLE_ARRAY_MEMBER];
} OldSnapshotTimeMapping;
#define NUM_TIME_MAPPING_COLUMNS 3
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(pg_old_snapshot_time_mapping);
static OldSnapshotTimeMapping *GetOldSnapshotTimeMapping(void);
static HeapTuple MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc,
OldSnapshotTimeMapping *mapping);
/*
* SQL-callable set-returning function.
*/
Datum
pg_old_snapshot_time_mapping(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
OldSnapshotTimeMapping *mapping;
if (SRF_IS_FIRSTCALL())
{
MemoryContext oldcontext;
TupleDesc tupdesc;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
mapping = GetOldSnapshotTimeMapping();
funcctx->user_fctx = mapping;
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
elog(ERROR, "return type must be a row type");
funcctx->tuple_desc = tupdesc;
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
mapping = (OldSnapshotTimeMapping *) funcctx->user_fctx;
while (mapping->current_index < mapping->count_used)
{
HeapTuple tuple;
tuple = MakeOldSnapshotTimeMappingTuple(funcctx->tuple_desc, mapping);
++mapping->current_index;
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
SRF_RETURN_DONE(funcctx);
}
/*
* Get the old snapshot time mapping data from shared memory.
*/
static OldSnapshotTimeMapping *
GetOldSnapshotTimeMapping(void)
{
OldSnapshotTimeMapping *mapping;
mapping = palloc(offsetof(OldSnapshotTimeMapping, xid_by_minute)
+ sizeof(TransactionId) * OLD_SNAPSHOT_TIME_MAP_ENTRIES);
mapping->current_index = 0;
LWLockAcquire(OldSnapshotTimeMapLock, LW_SHARED);
mapping->head_offset = oldSnapshotControl->head_offset;
mapping->head_timestamp = oldSnapshotControl->head_timestamp;
mapping->count_used = oldSnapshotControl->count_used;
for (int i = 0; i < OLD_SNAPSHOT_TIME_MAP_ENTRIES; ++i)
mapping->xid_by_minute[i] = oldSnapshotControl->xid_by_minute[i];
LWLockRelease(OldSnapshotTimeMapLock);
return mapping;
}
/*
* Convert one entry from the old snapshot time mapping to a HeapTuple.
*/
static HeapTuple
MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc, OldSnapshotTimeMapping *mapping)
{
Datum values[NUM_TIME_MAPPING_COLUMNS];
bool nulls[NUM_TIME_MAPPING_COLUMNS];
int array_position;
TimestampTz timestamp;
/*
* Figure out the array position corresponding to the current index.
*
* Index 0 means the oldest entry in the mapping, which is stored at
* mapping->head_offset. Index 1 means the next-oldest entry, which is a
* the following index, and so on. We wrap around when we reach the end of
* the array.
*/
array_position = (mapping->head_offset + mapping->current_index)
% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
/*
* No explicit timestamp is stored for any entry other than the oldest
* one, but each entry corresponds to 1-minute period, so we can just add.
*/
timestamp = TimestampTzPlusMilliseconds(mapping->head_timestamp,
mapping->current_index * 60000);
/* Initialize nulls and values arrays. */
memset(nulls, 0, sizeof(nulls));
values[0] = Int32GetDatum(array_position);
values[1] = TimestampTzGetDatum(timestamp);
values[2] = TransactionIdGetDatum(mapping->xid_by_minute[array_position]);
return heap_form_tuple(tupdesc, values, nulls);
}

69
doc/src/sgml/config.sgml
View File

@ -2709,65 +2709,6 @@ include_dir 'conf.d'
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-old-snapshot-threshold" xreflabel="old_snapshot_threshold">
<term><varname>old_snapshot_threshold</varname> (<type>integer</type>)
<indexterm>
<primary><varname>old_snapshot_threshold</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Sets the minimum amount of time that a query snapshot can be used
without risk of a <quote>snapshot too old</quote> error occurring
when using the snapshot. Data that has been dead for longer than
this threshold is allowed to be vacuumed away. This can help
prevent bloat in the face of snapshots which remain in use for a
long time. To prevent incorrect results due to cleanup of data which
would otherwise be visible to the snapshot, an error is generated
when the snapshot is older than this threshold and the snapshot is
used to read a page which has been modified since the snapshot was
built.
</para>
<para>
If this value is specified without units, it is taken as minutes.
A value of <literal>-1</literal> (the default) disables this feature,
effectively setting the snapshot age limit to infinity.
This parameter can only be set at server start.
</para>
<para>
Useful values for production work probably range from a small number
of hours to a few days. Small values (such as <literal>0</literal> or
<literal>1min</literal>) are only allowed because they may sometimes be
useful for testing. While a setting as high as <literal>60d</literal> is
allowed, please note that in many workloads extreme bloat or
transaction ID wraparound may occur in much shorter time frames.
</para>
<para>
When this feature is enabled, freed space at the end of a relation
cannot be released to the operating system, since that could remove
information needed to detect the <quote>snapshot too old</quote>
condition. All space allocated to a relation remains associated with
that relation for reuse only within that relation unless explicitly
freed (for example, with <command>VACUUM FULL</command>).
</para>
<para>
This setting does not attempt to guarantee that an error will be
generated under any particular circumstances. In fact, if the
correct results can be generated from (for example) a cursor which
has materialized a result set, no error will be generated even if the
underlying rows in the referenced table have been vacuumed away.
Some tables cannot safely be vacuumed early, and so will not be
affected by this setting, such as system catalogs. For such tables
this setting will neither reduce bloat nor create a possibility
of a <quote>snapshot too old</quote> error on scanning.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
@ -4783,16 +4724,6 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
until it eventually reaches the primary. Standbys make no other use
of feedback they receive other than to pass upstream.
</para>
<para>
This setting does not override the behavior of
<varname>old_snapshot_threshold</varname> on the primary; a snapshot on the
standby which exceeds the primary's age threshold can become invalid,
resulting in cancellation of transactions on the standby. This is
because <varname>old_snapshot_threshold</varname> is intended to provide an
absolute limit on the time which dead rows can contribute to bloat,
which would otherwise be violated because of the configuration of a
standby.
</para>
</listitem>
</varlistentry>

1
doc/src/sgml/contrib.sgml
View File

@ -150,7 +150,6 @@ CREATE EXTENSION <replaceable>extension_name</replaceable>;
&isn;
&lo;
&ltree;
&oldsnapshot;
&pageinspect;
&passwordcheck;
&pgbuffercache;

1
doc/src/sgml/filelist.sgml
View File

@ -138,7 +138,6 @@
<!ENTITY lo SYSTEM "lo.sgml">
<!ENTITY ltree SYSTEM "ltree.sgml">
<!ENTITY oid2name SYSTEM "oid2name.sgml">
<!ENTITY oldsnapshot SYSTEM "oldsnapshot.sgml">
<!ENTITY pageinspect SYSTEM "pageinspect.sgml">
<!ENTITY passwordcheck SYSTEM "passwordcheck.sgml">
<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">

33
doc/src/sgml/oldsnapshot.sgml
View File

@ -1,33 +0,0 @@
<!-- doc/src/sgml/oldsnapshot.sgml -->
<sect1 id="oldsnapshot" xreflabel="old_snapshot">
<title>old_snapshot &mdash; inspect <literal>old_snapshot_threshold</literal> state</title>
<indexterm zone="oldsnapshot">
<primary>old_snapshot</primary>
</indexterm>
<para>
The <filename>old_snapshot</filename> module allows inspection
of the server state that is used to implement
<xref linkend="guc-old-snapshot-threshold" />.
</para>
<sect2 id="oldsnapshot-functions">
<title>Functions</title>
<variablelist>
<varlistentry>
<term><function>pg_old_snapshot_time_mapping(array_offset OUT int4, end_timestamp OUT timestamptz, newest_xmin OUT xid) returns setof record</function></term>
<listitem>
<para>
Returns all of the entries in the server's timestamp to XID mapping.
Each entry represents the newest xmin of any snapshot taken in the
corresponding minute.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>

7
src/backend/access/brin/brin_revmap.c
View File

@ -79,7 +79,6 @@ brinRevmapInitialize(Relation idxrel, BlockNumber *pagesPerRange,
meta = ReadBuffer(idxrel, BRIN_METAPAGE_BLKNO);
LockBuffer(meta, BUFFER_LOCK_SHARE);
page = BufferGetPage(meta);
TestForOldSnapshot(snapshot, idxrel, page);
metadata = (BrinMetaPageData *) PageGetContents(page);
revmap = palloc(sizeof(BrinRevmap));
@ -277,7 +276,6 @@ brinGetTupleForHeapBlock(BrinRevmap *revmap, BlockNumber heapBlk,
}
LockBuffer(*buf, mode);
page = BufferGetPage(*buf);
TestForOldSnapshot(snapshot, idxRel, page);
/* If we land on a revmap page, start over */
if (BRIN_IS_REGULAR_PAGE(page))
@ -372,11 +370,6 @@ brinRevmapDesummarizeRange(Relation idxrel, BlockNumber heapBlk)
LockBuffer(regBuf, BUFFER_LOCK_EXCLUSIVE);
regPg = BufferGetPage(regBuf);
/*
* We're only removing data, not reading it, so there's no need to
* TestForOldSnapshot here.
*/
/* if this is no longer a regular page, tell caller to start over */
if (!BRIN_IS_REGULAR_PAGE(regPg))
{

2
src/backend/access/gin/ginbtree.c
View File

@ -100,7 +100,6 @@ ginFindLeafPage(GinBtree btree, bool searchMode,
stack->off = InvalidOffsetNumber;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
access = ginTraverseLock(stack->buffer, searchMode);
@ -127,7 +126,6 @@ ginFindLeafPage(GinBtree btree, bool searchMode,
stack->buffer = ginStepRight(stack->buffer, btree->index, access);
stack->blkno = rightlink;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
if (!searchMode && GinPageIsIncompleteSplit(page))
ginFinishSplit(btree, stack, false, NULL);

4
src/backend/access/gin/ginget.c
View File

@ -158,7 +158,6 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
return true;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, stack->off));
/*
@ -1460,7 +1459,6 @@ scanGetCandidate(IndexScanDesc scan, pendingPosition *pos)
for (;;)
{
page = BufferGetPage(pos->pendingBuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
maxoff = PageGetMaxOffsetNumber(page);
if (pos->firstOffset > maxoff)
@ -1641,7 +1639,6 @@ collectMatchesForHeapRow(IndexScanDesc scan, pendingPosition *pos)
sizeof(bool) * (pos->lastOffset - pos->firstOffset));
page = BufferGetPage(pos->pendingBuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
for (i = 0; i < so->nkeys; i++)
{
@ -1844,7 +1841,6 @@ scanPendingInsert(IndexScanDesc scan, TIDBitmap *tbm, int64 *ntids)
LockBuffer(metabuffer, GIN_SHARE);
page = BufferGetPage(metabuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
blkno = GinPageGetMeta(page)->head;
/*

1
src/backend/access/gist/gistget.c
View File

@ -346,7 +346,6 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
PredicateLockPage(r, BufferGetBlockNumber(buffer), scan->xs_snapshot);
gistcheckpage(scan->indexRelation, buffer);
page = BufferGetPage(buffer);
TestForOldSnapshot(scan->xs_snapshot, r, page);
opaque = GistPageGetOpaque(page);
/*

6
src/backend/access/hash/hashsearch.c
View File

@ -71,7 +71,6 @@ _hash_next(IndexScanDesc scan, ScanDirection dir)
if (BlockNumberIsValid(blkno))
{
buf = _hash_getbuf(rel, blkno, HASH_READ, LH_OVERFLOW_PAGE);
TestForOldSnapshot(scan->xs_snapshot, rel, BufferGetPage(buf));
if (!_hash_readpage(scan, &buf, dir))
end_of_scan = true;
}
@ -91,7 +90,6 @@ _hash_next(IndexScanDesc scan, ScanDirection dir)
{
buf = _hash_getbuf(rel, blkno, HASH_READ,
LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
TestForOldSnapshot(scan->xs_snapshot, rel, BufferGetPage(buf));
/*
* We always maintain the pin on bucket page for whole scan
@ -186,7 +184,6 @@ _hash_readnext(IndexScanDesc scan,
if (block_found)
{
*pagep = BufferGetPage(*bufp);
TestForOldSnapshot(scan->xs_snapshot, rel, *pagep);
*opaquep = HashPageGetOpaque(*pagep);
}
}
@ -232,7 +229,6 @@ _hash_readprev(IndexScanDesc scan,
*bufp = _hash_getbuf(rel, blkno, HASH_READ,
LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
*pagep = BufferGetPage(*bufp);
TestForOldSnapshot(scan->xs_snapshot, rel, *pagep);
*opaquep = HashPageGetOpaque(*pagep);
/*
@ -351,7 +347,6 @@ _hash_first(IndexScanDesc scan, ScanDirection dir)
buf = _hash_getbucketbuf_from_hashkey(rel, hashkey, HASH_READ, NULL);
PredicateLockPage(rel, BufferGetBlockNumber(buf), scan->xs_snapshot);
page = BufferGetPage(buf);
TestForOldSnapshot(scan->xs_snapshot, rel, page);
opaque = HashPageGetOpaque(page);
bucket = opaque->hasho_bucket;
@ -387,7 +382,6 @@ _hash_first(IndexScanDesc scan, ScanDirection dir)
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
old_buf = _hash_getbuf(rel, old_blkno, HASH_READ, LH_BUCKET_PAGE);
TestForOldSnapshot(scan->xs_snapshot, rel, BufferGetPage(old_buf));
/*
* remember the split bucket buffer so as to use it later for

9
src/backend/access/heap/heapam.c
View File

@ -425,7 +425,6 @@ heapgetpage(TableScanDesc sscan, BlockNumber block)
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
lines = PageGetMaxOffsetNumber(page);
ntup = 0;
@ -565,8 +564,6 @@ heapgettup_start_page(HeapScanDesc scan, ScanDirection dir, int *linesleft,
/* Caller is responsible for ensuring buffer is locked if needed */
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
*linesleft = PageGetMaxOffsetNumber(page) - FirstOffsetNumber + 1;
if (ScanDirectionIsForward(dir))
@ -598,8 +595,6 @@ heapgettup_continue_page(HeapScanDesc scan, ScanDirection dir, int *linesleft,
/* Caller is responsible for ensuring buffer is locked if needed */
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
if (ScanDirectionIsForward(dir))
{
*lineoff = OffsetNumberNext(scan->rs_coffset);
@ -864,7 +859,6 @@ heapgettup_pagemode(HeapScanDesc scan,
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
lineindex = scan->rs_cindex + dir;
if (ScanDirectionIsForward(dir))
@ -884,7 +878,6 @@ heapgettup_pagemode(HeapScanDesc scan,
{
heapgetpage((TableScanDesc) scan, block);
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
linesleft = scan->rs_ntuples;
lineindex = ScanDirectionIsForward(dir) ? 0 : linesleft - 1;
@ -1372,7 +1365,6 @@ heap_fetch(Relation relation,
*/
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
TestForOldSnapshot(snapshot, relation, page);
/*
* We'd better check for out-of-range offnum in case of VACUUM since the
@ -1663,7 +1655,6 @@ heap_get_latest_tid(TableScanDesc sscan,
buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
TestForOldSnapshot(snapshot, relation, page);
/*
* Check for bogus item number. This is not treated as an error

120
src/backend/access/heap/pruneheap.c
View File

@ -36,18 +36,6 @@ typedef struct
/* tuple visibility test, initialized for the relation */
GlobalVisState *vistest;
/*
* Thresholds set by TransactionIdLimitedForOldSnapshots() if they have
* been computed (done on demand, and only if
* OldSnapshotThresholdActive()). The first time a tuple is about to be
* removed based on the limited horizon, old_snap_used is set to true, and
* SetOldSnapshotThresholdTimestamp() is called. See
* heap_prune_satisfies_vacuum().
*/
TimestampTz old_snap_ts;
TransactionId old_snap_xmin;
bool old_snap_used;
TransactionId new_prune_xid; /* new prune hint value for page */
TransactionId snapshotConflictHorizon; /* latest xid removed */
int nredirected; /* numbers of entries in arrays below */
@ -110,8 +98,6 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
Page page = BufferGetPage(buffer);
TransactionId prune_xid;
GlobalVisState *vistest;
TransactionId limited_xmin = InvalidTransactionId;
TimestampTz limited_ts = 0;
Size minfree;
/*
@ -122,15 +108,6 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
if (RecoveryInProgress())
return;
/*
* XXX: Magic to keep old_snapshot_threshold tests appear "working". They
* currently are broken, and discussion of what to do about them is
* ongoing. See
* https://www.postgresql.org/message-id/20200403001235.e6jfdll3gh2ygbuc%40alap3.anarazel.de
*/
if (old_snapshot_threshold == 0)
SnapshotTooOldMagicForTest();
/*
* First check whether there's any chance there's something to prune,
* determining the appropriate horizon is a waste if there's no prune_xid
@ -143,35 +120,11 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
/*
* Check whether prune_xid indicates that there may be dead rows that can
* be cleaned up.
*
* It is OK to check the old snapshot limit before acquiring the cleanup
* lock because the worst that can happen is that we are not quite as
* aggressive about the cleanup (by however many transaction IDs are
* consumed between this point and acquiring the lock). This allows us to
* save significant overhead in the case where the page is found not to be
* prunable.
*
* Even if old_snapshot_threshold is set, we first check whether the page
* can be pruned without. Both because
* TransactionIdLimitedForOldSnapshots() is not cheap, and because not
* unnecessarily relying on old_snapshot_threshold avoids causing
* conflicts.
*/
vistest = GlobalVisTestFor(relation);
if (!GlobalVisTestIsRemovableXid(vistest, prune_xid))
{
if (!OldSnapshotThresholdActive())
return;
if (!TransactionIdLimitedForOldSnapshots(GlobalVisTestNonRemovableHorizon(vistest),
relation,
&limited_xmin, &limited_ts))
return;
if (!TransactionIdPrecedes(prune_xid, limited_xmin))
return;
}
return;
/*
* We prune when a previous UPDATE failed to find enough space on the page
@ -205,8 +158,8 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
int ndeleted,
nnewlpdead;
ndeleted = heap_page_prune(relation, buffer, vistest, limited_xmin,
limited_ts, &nnewlpdead, NULL);
ndeleted = heap_page_prune(relation, buffer, vistest,
&nnewlpdead, NULL);
/*
* Report the number of tuples reclaimed to pgstats. This is
@ -249,9 +202,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
*
* vistest is used to distinguish whether tuples are DEAD or RECENTLY_DEAD
* (see heap_prune_satisfies_vacuum and
* HeapTupleSatisfiesVacuum). old_snap_xmin / old_snap_ts need to
* either have been set by TransactionIdLimitedForOldSnapshots, or
* InvalidTransactionId/0 respectively.
* HeapTupleSatisfiesVacuum).
*
* Sets *nnewlpdead for caller, indicating the number of items that were
* newly set LP_DEAD during prune operation.
@ -264,8 +215,6 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
int
heap_page_prune(Relation relation, Buffer buffer,
GlobalVisState *vistest,
TransactionId old_snap_xmin,
TimestampTz old_snap_ts,
int *nnewlpdead,
OffsetNumber *off_loc)
{
@ -291,9 +240,6 @@ heap_page_prune(Relation relation, Buffer buffer,
prstate.new_prune_xid = InvalidTransactionId;
prstate.rel = relation;
prstate.vistest = vistest;
prstate.old_snap_xmin = old_snap_xmin;
prstate.old_snap_ts = old_snap_ts;
prstate.old_snap_used = false;
prstate.snapshotConflictHorizon = InvalidTransactionId;
prstate.nredirected = prstate.ndead = prstate.nunused = 0;
memset(prstate.marked, 0, sizeof(prstate.marked));
@ -481,19 +427,6 @@ heap_page_prune(Relation relation, Buffer buffer,
/*
* Perform visibility checks for heap pruning.
*
* This is more complicated than just using GlobalVisTestIsRemovableXid()
* because of old_snapshot_threshold. We only want to increase the threshold
* that triggers errors for old snapshots when we actually decide to remove a
* row based on the limited horizon.
*
* Due to its cost we also only want to call
* TransactionIdLimitedForOldSnapshots() if necessary, i.e. we might not have
* done so in heap_page_prune_opt() if pd_prune_xid was old enough. But we
* still want to be able to remove rows that are too new to be removed
* according to prstate->vistest, but that can be removed based on
* old_snapshot_threshold. So we call TransactionIdLimitedForOldSnapshots() on
* demand in here, if appropriate.
*/
static HTSV_Result
heap_prune_satisfies_vacuum(PruneState *prstate, HeapTuple tup, Buffer buffer)
@ -506,53 +439,8 @@ heap_prune_satisfies_vacuum(PruneState *prstate, HeapTuple tup, Buffer buffer)
if (res != HEAPTUPLE_RECENTLY_DEAD)
return res;
/*
* If we are already relying on the limited xmin, there is no need to
* delay doing so anymore.
*/
if (prstate->old_snap_used)
{
Assert(TransactionIdIsValid(prstate->old_snap_xmin));
if (TransactionIdPrecedes(dead_after, prstate->old_snap_xmin))
res = HEAPTUPLE_DEAD;
return res;
}
/*
* First check if GlobalVisTestIsRemovableXid() is sufficient to find the
* row dead. If not, and old_snapshot_threshold is enabled, try to use the
* lowered horizon.
*/
if (GlobalVisTestIsRemovableXid(prstate->vistest, dead_after))
res = HEAPTUPLE_DEAD;
else if (OldSnapshotThresholdActive())
{
/* haven't determined limited horizon yet, requests */
if (!TransactionIdIsValid(prstate->old_snap_xmin))
{
TransactionId horizon =
GlobalVisTestNonRemovableHorizon(prstate->vistest);
TransactionIdLimitedForOldSnapshots(horizon, prstate->rel,
&prstate->old_snap_xmin,
&prstate->old_snap_ts);
}
if (TransactionIdIsValid(prstate->old_snap_xmin) &&
TransactionIdPrecedes(dead_after, prstate->old_snap_xmin))
{
/*
* About to remove row based on snapshot_too_old. Need to raise
* the threshold so problematic accesses would error.
*/
Assert(!prstate->old_snap_used);
SetOldSnapshotThresholdTimestamp(prstate->old_snap_ts,
prstate->old_snap_xmin);
prstate->old_snap_used = true;
res = HEAPTUPLE_DEAD;
}
}
return res;
}

5
src/backend/access/heap/vacuumlazy.c
View File

@ -1588,7 +1588,7 @@ retry:
* that were deleted from indexes.
*/
tuples_deleted = heap_page_prune(rel, buf, vacrel->vistest,
InvalidTransactionId, 0, &nnewlpdead,
&nnewlpdead,
&vacrel->offnum);
/*
@ -2875,8 +2875,7 @@ should_attempt_truncation(LVRelState *vacrel)
{
BlockNumber possibly_freeable;
if (!vacrel->do_rel_truncate || VacuumFailsafeActive ||
old_snapshot_threshold >= 0)
if (!vacrel->do_rel_truncate || VacuumFailsafeActive)
return false;
possibly_freeable = vacrel->rel_pages - vacrel->nonempty_pages;

9
src/backend/access/nbtree/nbtsearch.c
View File

@ -278,7 +278,6 @@ _bt_moveright(Relation rel,
for (;;)
{
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
if (P_RIGHTMOST(opaque))
@ -2029,7 +2028,6 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir)
/* step right one page */
so->currPos.buf = _bt_getbuf(rel, blkno, BT_READ);
page = BufferGetPage(so->currPos.buf);
TestForOldSnapshot(scan->xs_snapshot, rel, page);
opaque = BTPageGetOpaque(page);
/* check for deleted page */
if (!P_IGNORE(opaque))
@ -2132,7 +2130,6 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir)
* and do it all again.
*/
page = BufferGetPage(so->currPos.buf);
TestForOldSnapshot(scan->xs_snapshot, rel, page);
opaque = BTPageGetOpaque(page);
if (!P_IGNORE(opaque))
{
@ -2238,7 +2235,6 @@ _bt_walk_left(Relation rel, Buffer buf, Snapshot snapshot)
CHECK_FOR_INTERRUPTS();
buf = _bt_getbuf(rel, blkno, BT_READ);
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
/*
@ -2265,14 +2261,12 @@ _bt_walk_left(Relation rel, Buffer buf, Snapshot snapshot)
blkno = opaque->btpo_next;
buf = _bt_relandgetbuf(rel, buf, blkno, BT_READ);
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
}
/* Return to the original page to see what's up */
buf = _bt_relandgetbuf(rel, buf, obknum, BT_READ);
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
if (P_ISDELETED(opaque))
{
@ -2290,7 +2284,6 @@ _bt_walk_left(Relation rel, Buffer buf, Snapshot snapshot)
blkno = opaque->btpo_next;
buf = _bt_relandgetbuf(rel, buf, blkno, BT_READ);
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
if (!P_ISDELETED(opaque))
break;
@ -2351,7 +2344,6 @@ _bt_get_endpoint(Relation rel, uint32 level, bool rightmost,
return InvalidBuffer;
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
for (;;)
@ -2371,7 +2363,6 @@ _bt_get_endpoint(Relation rel, uint32 level, bool rightmost,
RelationGetRelationName(rel));
buf = _bt_relandgetbuf(rel, buf, blkno, BT_READ);
page = BufferGetPage(buf);
TestForOldSnapshot(snapshot, rel, page);
opaque = BTPageGetOpaque(page);
}

1
src/backend/access/spgist/spgscan.c
View File

@ -862,7 +862,6 @@ redirect:
/* else new pointer points to the same page, no work needed */
page = BufferGetPage(buffer);
TestForOldSnapshot(snapshot, index, page);
isnull = SpGistPageStoresNulls(page) ? true : false;

28
src/backend/catalog/index.c
View File

@ -3048,12 +3048,11 @@ index_build(Relation heapRelation,
/*
* If we found any potentially broken HOT chains, mark the index as not
* being usable until the current transaction is below the event horizon.
* See src/backend/access/heap/README.HOT for discussion. Also set this
* if early pruning/vacuuming is enabled for the heap relation. While it
* might become safe to use the index earlier based on actual cleanup
* activity and other active transactions, the test for that would be much
* more complex and would require some form of blocking, so keep it simple
* and fast by just using the current transaction.
* See src/backend/access/heap/README.HOT for discussion. While it might
* become safe to use the index earlier based on actual cleanup activity
* and other active transactions, the test for that would be much more
* complex and would require some form of blocking, so keep it simple and
* fast by just using the current transaction.
*
* However, when reindexing an existing index, we should do nothing here.
* Any HOT chains that are broken with respect to the index must predate
@ -3065,7 +3064,7 @@ index_build(Relation heapRelation,
*
* We also need not set indcheckxmin during a concurrent index build,
* because we won't set indisvalid true until all transactions that care
* about the broken HOT chains or early pruning/vacuuming are gone.
* about the broken HOT chains are gone.
*
* Therefore, this code path can only be taken during non-concurrent
* CREATE INDEX. Thus the fact that heap_update will set the pg_index
@ -3074,7 +3073,7 @@ index_build(Relation heapRelation,
* about any concurrent readers of the tuple; no other transaction can see
* it yet.
*/
if ((indexInfo->ii_BrokenHotChain || EarlyPruningEnabled(heapRelation)) &&
if (indexInfo->ii_BrokenHotChain &&
!isreindex &&
!indexInfo->ii_Concurrent)
{
@ -3759,11 +3758,6 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
* reindexing pg_index itself, we must not try to update tuples in it.
* pg_index's indexes should always have these flags in their clean state,
* so that won't happen.
*
* If early pruning/vacuuming is enabled for the heap relation, the
* usability horizon must be advanced to the current transaction on every
* build or rebuild. pg_index is OK in this regard because catalog tables
* are not subject to early cleanup.
*/
if (!skipped_constraint)
{
@ -3771,7 +3765,6 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
HeapTuple indexTuple;
Form_pg_index indexForm;
bool index_bad;
bool early_pruning_enabled = EarlyPruningEnabled(heapRelation);
pg_index = table_open(IndexRelationId, RowExclusiveLock);
@ -3785,12 +3778,11 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
!indexForm->indisready ||
!indexForm->indislive);
if (index_bad ||
(indexForm->indcheckxmin && !indexInfo->ii_BrokenHotChain) ||
early_pruning_enabled)
(indexForm->indcheckxmin && !indexInfo->ii_BrokenHotChain))
{
if (!indexInfo->ii_BrokenHotChain && !early_pruning_enabled)
if (!indexInfo->ii_BrokenHotChain)
indexForm->indcheckxmin = false;
else if (index_bad || early_pruning_enabled)
else if (index_bad)
indexForm->indcheckxmin = true;
indexForm->indisvalid = true;
indexForm->indisready = true;

19
src/backend/commands/vacuum.c
View File

@ -1110,25 +1110,6 @@ vacuum_get_cutoffs(Relation rel, const VacuumParams *params,
*/
cutoffs->OldestXmin = GetOldestNonRemovableTransactionId(rel);
if (OldSnapshotThresholdActive())
{
TransactionId limit_xmin;
TimestampTz limit_ts;
if (TransactionIdLimitedForOldSnapshots(cutoffs->OldestXmin, rel,
&limit_xmin, &limit_ts))
{
/*
* TODO: We should only set the threshold if we are pruning on the
* basis of the increased limits. Not as crucial here as it is
* for opportunistic pruning (which often happens at a much higher
* frequency), but would still be a significant improvement.
*/
SetOldSnapshotThresholdTimestamp(limit_ts, limit_xmin);
cutoffs->OldestXmin = limit_xmin;
}
}
Assert(TransactionIdIsNormal(cutoffs->OldestXmin));
/* Acquire OldestMxact */

17
src/backend/storage/buffer/bufmgr.c
View File

@ -5575,20 +5575,3 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
wb_context->nr_pending = 0;
}
/*
* Implement slower/larger portions of TestForOldSnapshot
*
* Smaller/faster portions are put inline, but the entire set of logic is too
* big for that.
*/
void
TestForOldSnapshot_impl(Snapshot snapshot, Relation relation)
{
if (RelationAllowsEarlyPruning(relation)
&& (snapshot)->whenTaken < GetOldSnapshotThresholdTimestamp())
ereport(ERROR,
(errcode(ERRCODE_SNAPSHOT_TOO_OLD),
errmsg("snapshot too old")));
}

2
src/backend/storage/ipc/ipci.c
View File

@ -138,7 +138,6 @@ CalculateShmemSize(int *num_semaphores)
size = add_size(size, WalRcvShmemSize());
size = add_size(size, PgArchShmemSize());
size = add_size(size, ApplyLauncherShmemSize());
size = add_size(size, SnapMgrShmemSize());
size = add_size(size, BTreeShmemSize());
size = add_size(size, SyncScanShmemSize());
size = add_size(size, AsyncShmemSize());
@ -298,7 +297,6 @@ CreateSharedMemoryAndSemaphores(void)
/*
* Set up other modules that need some shared memory space
*/
SnapMgrInit();
BTreeShmemInit();
SyncScanShmemInit();
AsyncShmemInit();

36
src/backend/storage/ipc/procarray.c
View File

@ -2066,34 +2066,6 @@ GetMaxSnapshotSubxidCount(void)
return TOTAL_MAX_CACHED_SUBXIDS;
}
/*
* Initialize old_snapshot_threshold specific parts of a newly build snapshot.
*/
static void
GetSnapshotDataInitOldSnapshot(Snapshot snapshot)
{
if (!OldSnapshotThresholdActive())
{
/*
* If not using "snapshot too old" feature, fill related fields with
* dummy values that don't require any locking.
*/
snapshot->lsn = InvalidXLogRecPtr;
snapshot->whenTaken = 0;
}
else
{
/*
* Capture the current time and WAL stream location in case this
* snapshot becomes old enough to need to fall back on the special
* "old snapshot" logic.
*/
snapshot->lsn = GetXLogInsertRecPtr();
snapshot->whenTaken = GetSnapshotCurrentTimestamp();
MaintainOldSnapshotTimeMapping(snapshot->whenTaken, snapshot->xmin);
}
}
/*
* Helper function for GetSnapshotData() that checks if the bulk of the
* visibility information in the snapshot is still valid. If so, it updates
@ -2147,8 +2119,8 @@ GetSnapshotDataReuse(Snapshot snapshot)
snapshot->active_count = 0;
snapshot->regd_count = 0;
snapshot->copied = false;
GetSnapshotDataInitOldSnapshot(snapshot);
snapshot->lsn = InvalidXLogRecPtr;
snapshot->whenTaken = 0;
return true;
}
@ -2529,8 +2501,8 @@ GetSnapshotData(Snapshot snapshot)
snapshot->active_count = 0;
snapshot->regd_count = 0;
snapshot->copied = false;
GetSnapshotDataInitOldSnapshot(snapshot);
snapshot->lsn = InvalidXLogRecPtr;
snapshot->whenTaken = 0;
return snapshot;
}

2
src/backend/storage/lmgr/lwlocknames.txt
View File

@ -47,7 +47,7 @@ CommitTsSLRULock 38
CommitTsLock 39
ReplicationOriginLock 40
MultiXactTruncationLock 41
OldSnapshotTimeMapLock 42
# 42 was OldSnapshotTimeMapLock
LogicalRepWorkerLock 43
XactTruncationLock 44
# 45 was XactTruncationLock until removal of BackendRandomLock

1
src/backend/utils/activity/wait_event_names.txt
View File

@ -312,7 +312,6 @@ WAIT_EVENT_DOCONLY CommitTsSLRU "Waiting to access the commit timestamp SLRU cac
WAIT_EVENT_DOCONLY CommitTs "Waiting to read or update the last value set for a transaction commit timestamp."
WAIT_EVENT_DOCONLY ReplicationOrigin "Waiting to create, drop or use a replication origin."
WAIT_EVENT_DOCONLY MultiXactTruncation "Waiting to read or truncate multixact information."
WAIT_EVENT_DOCONLY OldSnapshotTimeMap "Waiting to read or update old snapshot control information."
WAIT_EVENT_DOCONLY LogicalRepWorker "Waiting to read or update the state of logical replication workers."
WAIT_EVENT_DOCONLY XactTruncation "Waiting to execute <function>pg_xact_status</function> or update the oldest transaction ID available to it."
WAIT_EVENT_DOCONLY WrapLimitsVacuum "Waiting to update limits on transaction id and multixact consumption."

4
src/backend/utils/errcodes.txt
View File

@ -439,10 +439,6 @@ Section: Class 58 - System Error (errors external to PostgreSQL itself)
58P01 E ERRCODE_UNDEFINED_FILE undefined_file
58P02 E ERRCODE_DUPLICATE_FILE duplicate_file
Section: Class 72 - Snapshot Failure
# (class borrowed from Oracle)
72000 E ERRCODE_SNAPSHOT_TOO_OLD snapshot_too_old
Section: Class F0 - Configuration File Error
# (PostgreSQL-specific error class)

11
src/backend/utils/misc/guc_tables.c
View File

@ -3282,17 +3282,6 @@ struct config_int ConfigureNamesInt[] =
check_autovacuum_work_mem, NULL, NULL
},
{
{"old_snapshot_threshold", PGC_POSTMASTER, RESOURCES_ASYNCHRONOUS,
gettext_noop("Time before a snapshot is too old to read pages changed after the snapshot was taken."),
gettext_noop("A value of -1 disables this feature."),
GUC_UNIT_MIN
},
&old_snapshot_threshold,
-1, -1, MINS_PER_HOUR * HOURS_PER_DAY * 60,
NULL, NULL, NULL
},
{
{"tcp_keepalives_idle", PGC_USERSET, CONN_AUTH_TCP,
gettext_noop("Time between issuing TCP keepalives."),

2
src/backend/utils/misc/postgresql.conf.sample
View File

@ -197,8 +197,6 @@
#max_parallel_workers = 8 # maximum number of max_worker_processes that
# can be used in parallel operations
#parallel_leader_participation = on
#old_snapshot_threshold = -1 # 1min-60d; -1 disables; 0 is immediate
# (change requires restart)
#------------------------------------------------------------------------------

468
src/backend/utils/time/snapmgr.c
View File

@ -65,7 +65,6 @@
#include "storage/spin.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/old_snapshot.h"
#include "utils/rel.h"
#include "utils/resowner_private.h"
#include "utils/snapmgr.h"
@ -73,14 +72,6 @@
#include "utils/timestamp.h"
/*
* GUC parameters
*/
int old_snapshot_threshold; /* number of minutes, -1 disables */
volatile OldSnapshotControlData *oldSnapshotControl;
/*
* CurrentSnapshot points to the only snapshot taken in transaction-snapshot
* mode, and to the latest one taken in a read-committed transaction.
@ -170,7 +161,6 @@ typedef struct ExportedSnapshot
static List *exportedSnapshots = NIL;
/* Prototypes for local functions */
static TimestampTz AlignTimestampToMinuteBoundary(TimestampTz ts);
static Snapshot CopySnapshot(Snapshot snapshot);
static void FreeSnapshot(Snapshot snapshot);
static void SnapshotResetXmin(void);
@ -194,50 +184,6 @@ typedef struct SerializedSnapshotData
XLogRecPtr lsn;
} SerializedSnapshotData;
Size
SnapMgrShmemSize(void)
{
Size size;
size = offsetof(OldSnapshotControlData, xid_by_minute);
if (old_snapshot_threshold > 0)
size = add_size(size, mul_size(sizeof(TransactionId),
OLD_SNAPSHOT_TIME_MAP_ENTRIES));
return size;
}
/*
* Initialize for managing old snapshot detection.
*/
void
SnapMgrInit(void)
{
bool found;
/*
* Create or attach to the OldSnapshotControlData structure.
*/
oldSnapshotControl = (volatile OldSnapshotControlData *)
ShmemInitStruct("OldSnapshotControlData",
SnapMgrShmemSize(), &found);
if (!found)
{
SpinLockInit(&oldSnapshotControl->mutex_current);
oldSnapshotControl->current_timestamp = 0;
SpinLockInit(&oldSnapshotControl->mutex_latest_xmin);
oldSnapshotControl->latest_xmin = InvalidTransactionId;
oldSnapshotControl->next_map_update = 0;
SpinLockInit(&oldSnapshotControl->mutex_threshold);
oldSnapshotControl->threshold_timestamp = 0;
oldSnapshotControl->threshold_xid = InvalidTransactionId;
oldSnapshotControl->head_offset = 0;
oldSnapshotControl->head_timestamp = 0;
oldSnapshotControl->count_used = 0;
}
}
/*
* GetTransactionSnapshot
* Get the appropriate snapshot for a new query in a transaction.
@ -1656,420 +1602,6 @@ HaveRegisteredOrActiveSnapshot(void)
}
/*
* Return a timestamp that is exactly on a minute boundary.
*
* If the argument is already aligned, return that value, otherwise move to
* the next minute boundary following the given time.
*/
static TimestampTz
AlignTimestampToMinuteBoundary(TimestampTz ts)
{
TimestampTz retval = ts + (USECS_PER_MINUTE - 1);
return retval - (retval % USECS_PER_MINUTE);
}
/*
* Get current timestamp for snapshots
*
* This is basically GetCurrentTimestamp(), but with a guarantee that
* the result never moves backward.
*/
TimestampTz
GetSnapshotCurrentTimestamp(void)
{
TimestampTz now = GetCurrentTimestamp();
/*
* Don't let time move backward; if it hasn't advanced, use the old value.
*/
SpinLockAcquire(&oldSnapshotControl->mutex_current);
if (now <= oldSnapshotControl->current_timestamp)
now = oldSnapshotControl->current_timestamp;
else
oldSnapshotControl->current_timestamp = now;
SpinLockRelease(&oldSnapshotControl->mutex_current);
return now;
}
/*
* Get timestamp through which vacuum may have processed based on last stored
* value for threshold_timestamp.
*
* XXX: So far, we never trust that a 64-bit value can be read atomically; if
* that ever changes, we could get rid of the spinlock here.
*/
TimestampTz
GetOldSnapshotThresholdTimestamp(void)
{
TimestampTz threshold_timestamp;
SpinLockAcquire(&oldSnapshotControl->mutex_threshold);
threshold_timestamp = oldSnapshotControl->threshold_timestamp;
SpinLockRelease(&oldSnapshotControl->mutex_threshold);
return threshold_timestamp;
}
void
SetOldSnapshotThresholdTimestamp(TimestampTz ts, TransactionId xlimit)
{
SpinLockAcquire(&oldSnapshotControl->mutex_threshold);
Assert(oldSnapshotControl->threshold_timestamp <= ts);
Assert(TransactionIdPrecedesOrEquals(oldSnapshotControl->threshold_xid, xlimit));
oldSnapshotControl->threshold_timestamp = ts;
oldSnapshotControl->threshold_xid = xlimit;
SpinLockRelease(&oldSnapshotControl->mutex_threshold);
}
/*
* XXX: Magic to keep old_snapshot_threshold tests appear "working". They
* currently are broken, and discussion of what to do about them is
* ongoing. See
* https://www.postgresql.org/message-id/20200403001235.e6jfdll3gh2ygbuc%40alap3.anarazel.de
*/
void
SnapshotTooOldMagicForTest(void)
{
TimestampTz ts = GetSnapshotCurrentTimestamp();
Assert(old_snapshot_threshold == 0);
ts -= 5 * USECS_PER_SEC;
SpinLockAcquire(&oldSnapshotControl->mutex_threshold);
oldSnapshotControl->threshold_timestamp = ts;
SpinLockRelease(&oldSnapshotControl->mutex_threshold);
}
/*
* If there is a valid mapping for the timestamp, set *xlimitp to
* that. Returns whether there is such a mapping.
*/
static bool
GetOldSnapshotFromTimeMapping(TimestampTz ts, TransactionId *xlimitp)
{
bool in_mapping = false;
Assert(ts == AlignTimestampToMinuteBoundary(ts));
LWLockAcquire(OldSnapshotTimeMapLock, LW_SHARED);
if (oldSnapshotControl->count_used > 0
&& ts >= oldSnapshotControl->head_timestamp)
{
int offset;
offset = ((ts - oldSnapshotControl->head_timestamp)
/ USECS_PER_MINUTE);
if (offset > oldSnapshotControl->count_used - 1)
offset = oldSnapshotControl->count_used - 1;
offset = (oldSnapshotControl->head_offset + offset)
% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
*xlimitp = oldSnapshotControl->xid_by_minute[offset];
in_mapping = true;
}
LWLockRelease(OldSnapshotTimeMapLock);
return in_mapping;
}
/*
* TransactionIdLimitedForOldSnapshots
*
* Apply old snapshot limit. This is intended to be called for page pruning
* and table vacuuming, to allow old_snapshot_threshold to override the normal
* global xmin value. Actual testing for snapshot too old will be based on
* whether a snapshot timestamp is prior to the threshold timestamp set in
* this function.
*
* If the limited horizon allows a cleanup action that otherwise would not be
* possible, SetOldSnapshotThresholdTimestamp(*limit_ts, *limit_xid) needs to
* be called before that cleanup action.
*/
bool
TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
Relation relation,
TransactionId *limit_xid,
TimestampTz *limit_ts)
{
TimestampTz ts;
TransactionId xlimit = recentXmin;
TransactionId latest_xmin;
TimestampTz next_map_update_ts;
TransactionId threshold_timestamp;
TransactionId threshold_xid;
Assert(TransactionIdIsNormal(recentXmin));
Assert(OldSnapshotThresholdActive());
Assert(limit_ts != NULL && limit_xid != NULL);
/*
* TestForOldSnapshot() assumes early pruning advances the page LSN, so we
* can't prune early when skipping WAL.
*/
if (!RelationAllowsEarlyPruning(relation) || !RelationNeedsWAL(relation))
return false;
ts = GetSnapshotCurrentTimestamp();
SpinLockAcquire(&oldSnapshotControl->mutex_latest_xmin);
latest_xmin = oldSnapshotControl->latest_xmin;
next_map_update_ts = oldSnapshotControl->next_map_update;
SpinLockRelease(&oldSnapshotControl->mutex_latest_xmin);
/*
* Zero threshold always overrides to latest xmin, if valid. Without some
* heuristic it will find its own snapshot too old on, for example, a
* simple UPDATE -- which would make it useless for most testing, but
* there is no principled way to ensure that it doesn't fail in this way.
* Use a five-second delay to try to get useful testing behavior, but this
* may need adjustment.
*/
if (old_snapshot_threshold == 0)
{
if (TransactionIdPrecedes(latest_xmin, MyProc->xmin)
&& TransactionIdFollows(latest_xmin, xlimit))
xlimit = latest_xmin;
ts -= 5 * USECS_PER_SEC;
}
else
{
ts = AlignTimestampToMinuteBoundary(ts)
- (old_snapshot_threshold * USECS_PER_MINUTE);
/* Check for fast exit without LW locking. */
SpinLockAcquire(&oldSnapshotControl->mutex_threshold);
threshold_timestamp = oldSnapshotControl->threshold_timestamp;
threshold_xid = oldSnapshotControl->threshold_xid;
SpinLockRelease(&oldSnapshotControl->mutex_threshold);
if (ts == threshold_timestamp)
{
/*
* Current timestamp is in same bucket as the last limit that was
* applied. Reuse.
*/
xlimit = threshold_xid;
}
else if (ts == next_map_update_ts)
{
/*
* FIXME: This branch is super iffy - but that should probably
* fixed separately.
*/
xlimit = latest_xmin;
}
else if (GetOldSnapshotFromTimeMapping(ts, &xlimit))
{
}
/*
* Failsafe protection against vacuuming work of active transaction.
*
* This is not an assertion because we avoid the spinlock for
* performance, leaving open the possibility that xlimit could advance
* and be more current; but it seems prudent to apply this limit. It
* might make pruning a tiny bit less aggressive than it could be, but
* protects against data loss bugs.
*/
if (TransactionIdIsNormal(latest_xmin)
&& TransactionIdPrecedes(latest_xmin, xlimit))
xlimit = latest_xmin;
}
if (TransactionIdIsValid(xlimit) &&
TransactionIdFollowsOrEquals(xlimit, recentXmin))
{
*limit_ts = ts;
*limit_xid = xlimit;
return true;
}
return false;
}
/*
* Take care of the circular buffer that maps time to xid.
*/
void
MaintainOldSnapshotTimeMapping(TimestampTz whenTaken, TransactionId xmin)
{
TimestampTz ts;
TransactionId latest_xmin;
TimestampTz update_ts;
bool map_update_required = false;
/* Never call this function when old snapshot checking is disabled. */
Assert(old_snapshot_threshold >= 0);
ts = AlignTimestampToMinuteBoundary(whenTaken);
/*
* Keep track of the latest xmin seen by any process. Update mapping with
* a new value when we have crossed a bucket boundary.
*/
SpinLockAcquire(&oldSnapshotControl->mutex_latest_xmin);
latest_xmin = oldSnapshotControl->latest_xmin;
update_ts = oldSnapshotControl->next_map_update;
if (ts > update_ts)
{
oldSnapshotControl->next_map_update = ts;
map_update_required = true;
}
if (TransactionIdFollows(xmin, latest_xmin))
oldSnapshotControl->latest_xmin = xmin;
SpinLockRelease(&oldSnapshotControl->mutex_latest_xmin);
/* We only needed to update the most recent xmin value. */
if (!map_update_required)
return;
/* No further tracking needed for 0 (used for testing). */
if (old_snapshot_threshold == 0)
return;
/*
* We don't want to do something stupid with unusual values, but we don't
* want to litter the log with warnings or break otherwise normal
* processing for this feature; so if something seems unreasonable, just
* log at DEBUG level and return without doing anything.
*/
if (whenTaken < 0)
{
elog(DEBUG1,
"MaintainOldSnapshotTimeMapping called with negative whenTaken = %ld",
(long) whenTaken);
return;
}
if (!TransactionIdIsNormal(xmin))
{
elog(DEBUG1,
"MaintainOldSnapshotTimeMapping called with xmin = %lu",
(unsigned long) xmin);
return;
}
LWLockAcquire(OldSnapshotTimeMapLock, LW_EXCLUSIVE);
Assert(oldSnapshotControl->head_offset >= 0);
Assert(oldSnapshotControl->head_offset < OLD_SNAPSHOT_TIME_MAP_ENTRIES);
Assert((oldSnapshotControl->head_timestamp % USECS_PER_MINUTE) == 0);
Assert(oldSnapshotControl->count_used >= 0);
Assert(oldSnapshotControl->count_used <= OLD_SNAPSHOT_TIME_MAP_ENTRIES);
if (oldSnapshotControl->count_used == 0)
{
/* set up first entry for empty mapping */
oldSnapshotControl->head_offset = 0;
oldSnapshotControl->head_timestamp = ts;
oldSnapshotControl->count_used = 1;
oldSnapshotControl->xid_by_minute[0] = xmin;
}
else if (ts < oldSnapshotControl->head_timestamp)
{
/* old ts; log it at DEBUG */
LWLockRelease(OldSnapshotTimeMapLock);
elog(DEBUG1,
"MaintainOldSnapshotTimeMapping called with old whenTaken = %ld",
(long) whenTaken);
return;
}
else if (ts <= (oldSnapshotControl->head_timestamp +
((oldSnapshotControl->count_used - 1)
* USECS_PER_MINUTE)))
{
/* existing mapping; advance xid if possible */
int bucket = (oldSnapshotControl->head_offset
+ ((ts - oldSnapshotControl->head_timestamp)
/ USECS_PER_MINUTE))
% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
if (TransactionIdPrecedes(oldSnapshotControl->xid_by_minute[bucket], xmin))
oldSnapshotControl->xid_by_minute[bucket] = xmin;
}
else
{
/* We need a new bucket, but it might not be the very next one. */
int distance_to_new_tail;
int distance_to_current_tail;
int advance;
/*
* Our goal is for the new "tail" of the mapping, that is, the entry
* which is newest and thus furthest from the "head" entry, to
* correspond to "ts". Since there's one entry per minute, the
* distance between the current head and the new tail is just the
* number of minutes of difference between ts and the current
* head_timestamp.
*
* The distance from the current head to the current tail is one less
* than the number of entries in the mapping, because the entry at the
* head_offset is for 0 minutes after head_timestamp.
*
* The difference between these two values is the number of minutes by
* which we need to advance the mapping, either adding new entries or
* rotating old ones out.
*/
distance_to_new_tail =
(ts - oldSnapshotControl->head_timestamp) / USECS_PER_MINUTE;
distance_to_current_tail =
oldSnapshotControl->count_used - 1;
advance = distance_to_new_tail - distance_to_current_tail;
Assert(advance > 0);
if (advance >= OLD_SNAPSHOT_TIME_MAP_ENTRIES)
{
/* Advance is so far that all old data is junk; start over. */
oldSnapshotControl->head_offset = 0;
oldSnapshotControl->count_used = 1;
oldSnapshotControl->xid_by_minute[0] = xmin;
oldSnapshotControl->head_timestamp = ts;
}
else
{
/* Store the new value in one or more buckets. */
int i;
for (i = 0; i < advance; i++)
{
if (oldSnapshotControl->count_used == OLD_SNAPSHOT_TIME_MAP_ENTRIES)
{
/* Map full and new value replaces old head. */
int old_head = oldSnapshotControl->head_offset;
if (old_head == (OLD_SNAPSHOT_TIME_MAP_ENTRIES - 1))
oldSnapshotControl->head_offset = 0;
else
oldSnapshotControl->head_offset = old_head + 1;
oldSnapshotControl->xid_by_minute[old_head] = xmin;
oldSnapshotControl->head_timestamp += USECS_PER_MINUTE;
}
else
{
/* Extend map to unused entry. */
int new_tail = (oldSnapshotControl->head_offset
+ oldSnapshotControl->count_used)
% OLD_SNAPSHOT_TIME_MAP_ENTRIES;
oldSnapshotControl->count_used++;
oldSnapshotControl->xid_by_minute[new_tail] = xmin;
}
}
}
}
LWLockRelease(OldSnapshotTimeMapLock);
}
/*
* Setup a snapshot that replaces normal catalog snapshots that allows catalog
* access to behave just like it did at a certain point in the past.

2
src/include/access/heapam.h
View File

@ -286,8 +286,6 @@ struct GlobalVisState;
extern void heap_page_prune_opt(Relation relation, Buffer buffer);
extern int heap_page_prune(Relation relation, Buffer buffer,
struct GlobalVisState *vistest,
TransactionId old_snap_xmin,
TimestampTz old_snap_ts,
int *nnewlpdead,
OffsetNumber *off_loc);
extern void heap_page_prune_execute(Buffer buffer,

36
src/include/storage/bufmgr.h
View File

@ -250,8 +250,6 @@ extern void AbortBufferIO(Buffer buffer);
extern bool BgBufferSync(struct WritebackContext *wb_context);
extern void TestForOldSnapshot_impl(Snapshot snapshot, Relation relation);
/* in buf_init.c */
extern void InitBufferPool(void);
extern Size BufferShmemSize(void);
@ -347,9 +345,6 @@ BufferGetPageSize(Buffer buffer)
/*
* BufferGetPage
* Returns the page associated with a buffer.
*
* When this is called as part of a scan, there may be a need for a nearby
* call to TestForOldSnapshot(). See the definition of that for details.
*/
static inline Page
BufferGetPage(Buffer buffer)
@ -357,37 +352,6 @@ BufferGetPage(Buffer buffer)
return (Page) BufferGetBlock(buffer);
}
/*
* Check whether the given snapshot is too old to have safely read the given
* page from the given table. If so, throw a "snapshot too old" error.
*
* This test generally needs to be performed after every BufferGetPage() call
* that is executed as part of a scan. It is not needed for calls made for
* modifying the page (for example, to position to the right place to insert a
* new index tuple or for vacuuming). It may also be omitted where calls to
* lower-level functions will have already performed the test.
*
* Note that a NULL snapshot argument is allowed and causes a fast return
* without error; this is to support call sites which can be called from
* either scans or index modification areas.
*
* For best performance, keep the tests that are fastest and/or most likely to
* exclude a page from old snapshot testing near the front.
*/
static inline void
TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page)
{
Assert(relation != NULL);
if (old_snapshot_threshold >= 0
&& (snapshot) != NULL
&& ((snapshot)->snapshot_type == SNAPSHOT_MVCC
|| (snapshot)->snapshot_type == SNAPSHOT_TOAST)
&& !XLogRecPtrIsInvalid((snapshot)->lsn)
&& PageGetLSN(page) > (snapshot)->lsn)
TestForOldSnapshot_impl(snapshot, relation);
}
#endif /* FRONTEND */
#endif /* BUFMGR_H */

75
src/include/utils/old_snapshot.h
View File

@ -1,75 +0,0 @@
/*-------------------------------------------------------------------------
*
* old_snapshot.h
* Data structures for 'snapshot too old'
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/include/utils/old_snapshot.h
*
*-------------------------------------------------------------------------
*/
#ifndef OLD_SNAPSHOT_H
#define OLD_SNAPSHOT_H
#include "datatype/timestamp.h"
#include "storage/s_lock.h"
/*
* Structure for dealing with old_snapshot_threshold implementation.
*/
typedef struct OldSnapshotControlData
{
/*
* Variables for old snapshot handling are shared among processes and are
* only allowed to move forward.
*/
slock_t mutex_current; /* protect current_timestamp */
TimestampTz current_timestamp; /* latest snapshot timestamp */
slock_t mutex_latest_xmin; /* protect latest_xmin and next_map_update */
TransactionId latest_xmin; /* latest snapshot xmin */
TimestampTz next_map_update; /* latest snapshot valid up to */
slock_t mutex_threshold; /* protect threshold fields */
TimestampTz threshold_timestamp; /* earlier snapshot is old */
TransactionId threshold_xid; /* earlier xid may be gone */
/*
* Keep one xid per minute for old snapshot error handling.
*
* Use a circular buffer with a head offset, a count of entries currently
* used, and a timestamp corresponding to the xid at the head offset. A
* count_used value of zero means that there are no times stored; a
* count_used value of OLD_SNAPSHOT_TIME_MAP_ENTRIES means that the buffer
* is full and the head must be advanced to add new entries. Use
* timestamps aligned to minute boundaries, since that seems less
* surprising than aligning based on the first usage timestamp. The
* latest bucket is effectively stored within latest_xmin. The circular
* buffer is updated when we get a new xmin value that doesn't fall into
* the same interval.
*
* It is OK if the xid for a given time slot is from earlier than
* calculated by adding the number of minutes corresponding to the
* (possibly wrapped) distance from the head offset to the time of the
* head entry, since that just results in the vacuuming of old tuples
* being slightly less aggressive. It would not be OK for it to be off in
* the other direction, since it might result in vacuuming tuples that are
* still expected to be there.
*
* Use of an SLRU was considered but not chosen because it is more
* heavyweight than is needed for this, and would probably not be any less
* code to implement.
*
* Persistence is not needed.
*/
int head_offset; /* subscript of oldest tracked time */
TimestampTz head_timestamp; /* time corresponding to head xid */
int count_used; /* how many slots are in use */
TransactionId xid_by_minute[FLEXIBLE_ARRAY_MEMBER];
} OldSnapshotControlData;
extern PGDLLIMPORT volatile OldSnapshotControlData *oldSnapshotControl;
#endif

49
src/include/utils/snapmgr.h
View File

@ -19,40 +19,6 @@
#include "utils/snapshot.h"
/*
* The structure used to map times to TransactionId values for the "snapshot
* too old" feature must have a few entries at the tail to hold old values;
* otherwise the lookup will often fail and the expected early pruning or
* vacuum will not usually occur. It is best if this padding is for a number
* of minutes greater than a thread would normally be stalled, but it's OK if
* early vacuum opportunities are occasionally missed, so there's no need to
* use an extreme value or get too fancy. 10 minutes seems plenty.
*/
#define OLD_SNAPSHOT_PADDING_ENTRIES 10
#define OLD_SNAPSHOT_TIME_MAP_ENTRIES (old_snapshot_threshold + OLD_SNAPSHOT_PADDING_ENTRIES)
/*
* Common definition of relation properties that allow early pruning/vacuuming
* when old_snapshot_threshold >= 0.
*/
#define RelationAllowsEarlyPruning(rel) \
( \
RelationIsPermanent(rel) && !IsCatalogRelation(rel) \
&& !RelationIsAccessibleInLogicalDecoding(rel) \
)
#define EarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))
/* GUC variables */
extern PGDLLIMPORT int old_snapshot_threshold;
extern Size SnapMgrShmemSize(void);
extern void SnapMgrInit(void);
extern TimestampTz GetSnapshotCurrentTimestamp(void);
extern TimestampTz GetOldSnapshotThresholdTimestamp(void);
extern void SnapshotTooOldMagicForTest(void);
extern PGDLLIMPORT bool FirstSnapshotSet;
extern PGDLLIMPORT TransactionId TransactionXmin;
@ -97,14 +63,6 @@ extern PGDLLIMPORT SnapshotData CatalogSnapshotData;
((snapshot)->snapshot_type == SNAPSHOT_MVCC || \
(snapshot)->snapshot_type == SNAPSHOT_HISTORIC_MVCC)
#ifndef FRONTEND
static inline bool
OldSnapshotThresholdActive(void)
{
return old_snapshot_threshold >= 0;
}
#endif
extern Snapshot GetTransactionSnapshot(void);
extern Snapshot GetLatestSnapshot(void);
extern void SnapshotSetCommandId(CommandId curcid);
@ -138,13 +96,6 @@ extern void DeleteAllExportedSnapshotFiles(void);
extern void WaitForOlderSnapshots(TransactionId limitXmin, bool progress);
extern bool ThereAreNoPriorRegisteredSnapshots(void);
extern bool HaveRegisteredOrActiveSnapshot(void);
extern bool TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
Relation relation,
TransactionId *limit_xid,
TimestampTz *limit_ts);
extern void SetOldSnapshotThresholdTimestamp(TimestampTz ts, TransactionId xlimit);
extern void MaintainOldSnapshotTimeMapping(TimestampTz whenTaken,
TransactionId xmin);
extern char *ExportSnapshot(Snapshot snapshot);

1
src/test/modules/Makefile
View File

@ -12,7 +12,6 @@ SUBDIRS = \
dummy_seclabel \
libpq_pipeline \
plsample \
snapshot_too_old \
spgist_name_ops \
test_bloomfilter \
test_copy_callbacks \

1
src/test/modules/meson.build
View File

@ -8,7 +8,6 @@ subdir('dummy_seclabel')
subdir('ldap_password_func')
subdir('libpq_pipeline')
subdir('plsample')
subdir('snapshot_too_old')
subdir('spgist_name_ops')
subdir('ssl_passphrase_callback')
subdir('test_bloomfilter')

3
src/test/modules/snapshot_too_old/.gitignore vendored
View File

@ -1,3 +0,0 @@
# Generated subdirectories
/output_iso/
/tmp_check_iso/

28
src/test/modules/snapshot_too_old/Makefile
View File

@ -1,28 +0,0 @@
# src/test/modules/snapshot_too_old/Makefile
# Note: because we don't tell the Makefile there are any regression tests,
# we have to clean those result files explicitly
EXTRA_CLEAN = $(pg_regress_clean_files)
ISOLATION = sto_using_cursor sto_using_select sto_using_hash_index
ISOLATION_OPTS = --temp-config $(top_srcdir)/src/test/modules/snapshot_too_old/sto.conf
# Disabled because these tests require "old_snapshot_threshold" >= 0, which
# typical installcheck users do not have (e.g. buildfarm clients).
NO_INSTALLCHECK = 1
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = src/test/modules/snapshot_too_old
top_builddir = ../../../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif
# But it can nonetheless be very helpful to run tests on preexisting
# installation, allow to do so, but only if requested explicitly.
installcheck-force:
$(pg_isolation_regress_installcheck) $(ISOLATION)

19
src/test/modules/snapshot_too_old/expected/sto_using_cursor.out
View File

@ -1,19 +0,0 @@
Parsed test spec with 2 sessions
starting permutation: s1decl s1f1 s1sleep s2u s1f2
step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
step s1f1: FETCH FIRST FROM cursor1;
c
-
1
(1 row)
step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
setting|pg_sleep
-------+--------
0|
(1 row)
step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
step s1f2: FETCH FIRST FROM cursor1;
ERROR: snapshot too old

19
src/test/modules/snapshot_too_old/expected/sto_using_hash_index.out
View File

@ -1,19 +0,0 @@
Parsed test spec with 2 sessions
starting permutation: noseq s1f1 s2sleep s2u s1f2
step noseq: SET enable_seqscan = false;
step s1f1: SELECT c FROM sto1 where c = 1000;
c
----
1000
(1 row)
step s2sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
setting|pg_sleep
-------+--------
0|
(1 row)
step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1000;
step s1f2: SELECT c FROM sto1 where c = 1001;
ERROR: snapshot too old

18
src/test/modules/snapshot_too_old/expected/sto_using_select.out
View File

@ -1,18 +0,0 @@
Parsed test spec with 2 sessions
starting permutation: s1f1 s1sleep s2u s1f2
step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
c
-
1
(1 row)
step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
setting|pg_sleep
-------+--------
0|
(1 row)
step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
ERROR: snapshot too old

19
src/test/modules/snapshot_too_old/meson.build
View File

@ -1,19 +0,0 @@
# Copyright (c) 2022-2023, PostgreSQL Global Development Group
tests += {
'name': 'snapshot_too_old',
'sd': meson.current_source_dir(),
'bd': meson.current_build_dir(),
'isolation': {
'test_kwargs': {'priority': 40}, # sto tests are slow, start early
'specs': [
'sto_using_cursor',
'sto_using_select',
'sto_using_hash_index',
],
'regress_args': ['--temp-config', files('sto.conf')],
# Disabled because these tests require "old_snapshot_threshold" >= 0, which
# typical runningcheck users do not have (e.g. buildfarm clients).
'runningcheck': false,
},
}

38
src/test/modules/snapshot_too_old/specs/sto_using_cursor.spec
View File

@ -1,38 +0,0 @@
# This test provokes a "snapshot too old" error using a cursor.
#
# The sleep is needed because with a threshold of zero a statement could error
# on changes it made. With more normal settings no external delay is needed,
# but we don't want these tests to run long enough to see that, since
# granularity is in minutes.
#
# Since results depend on the value of old_snapshot_threshold, sneak that into
# the line generated by the sleep, so that a surprising value isn't so hard
# to identify.
setup
{
CREATE TABLE sto1 (c int NOT NULL);
INSERT INTO sto1 SELECT generate_series(1, 1000);
}
setup
{
VACUUM ANALYZE sto1;
}
teardown
{
DROP TABLE sto1;
}
session "s1"
setup { BEGIN ISOLATION LEVEL REPEATABLE READ; }
step "s1decl" { DECLARE cursor1 CURSOR FOR SELECT c FROM sto1; }
step "s1f1" { FETCH FIRST FROM cursor1; }
step "s1sleep" { SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold'; }
step "s1f2" { FETCH FIRST FROM cursor1; }
teardown { COMMIT; }
session "s2"
step "s2u" { UPDATE sto1 SET c = 1001 WHERE c = 1; }
permutation "s1decl" "s1f1" "s1sleep" "s2u" "s1f2"

31
src/test/modules/snapshot_too_old/specs/sto_using_hash_index.spec
View File

@ -1,31 +0,0 @@
# This test is like sto_using_select, except that we test access via a
# hash index.
setup
{
CREATE TABLE sto1 (c int NOT NULL);
INSERT INTO sto1 SELECT generate_series(1, 1000);
CREATE INDEX idx_sto1 ON sto1 USING HASH (c);
}
setup
{
VACUUM ANALYZE sto1;
}
teardown
{
DROP TABLE sto1;
}
session "s1"
setup { BEGIN ISOLATION LEVEL REPEATABLE READ; }
step "noseq" { SET enable_seqscan = false; }
step "s1f1" { SELECT c FROM sto1 where c = 1000; }
step "s1f2" { SELECT c FROM sto1 where c = 1001; }
teardown { ROLLBACK; }
session "s2"
step "s2sleep" { SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold'; }
step "s2u" { UPDATE sto1 SET c = 1001 WHERE c = 1000; }
permutation "noseq" "s1f1" "s2sleep" "s2u" "s1f2"

37
src/test/modules/snapshot_too_old/specs/sto_using_select.spec
View File

@ -1,37 +0,0 @@
# This test provokes a "snapshot too old" error using SELECT statements.
#
# The sleep is needed because with a threshold of zero a statement could error
# on changes it made. With more normal settings no external delay is needed,
# but we don't want these tests to run long enough to see that, since
# granularity is in minutes.
#
# Since results depend on the value of old_snapshot_threshold, sneak that into
# the line generated by the sleep, so that a surprising value isn't so hard
# to identify.
setup
{
CREATE TABLE sto1 (c int NOT NULL);
INSERT INTO sto1 SELECT generate_series(1, 1000);
}
setup
{
VACUUM ANALYZE sto1;
}
teardown
{
DROP TABLE sto1;
}
session "s1"
setup { BEGIN ISOLATION LEVEL REPEATABLE READ; }
step "s1f1" { SELECT c FROM sto1 ORDER BY c LIMIT 1; }
step "s1sleep" { SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold'; }
step "s1f2" { SELECT c FROM sto1 ORDER BY c LIMIT 1; }
teardown { COMMIT; }
session "s2"
step "s2u" { UPDATE sto1 SET c = 1001 WHERE c = 1; }
permutation "s1f1" "s1sleep" "s2u" "s1f2"

2
src/test/modules/snapshot_too_old/sto.conf
View File

@ -1,2 +0,0 @@
autovacuum = off
old_snapshot_threshold = 0

2
src/tools/pgindent/typedefs.list
View File

@ -1659,8 +1659,6 @@ OffsetVarNodes_context
Oid
OidOptions
OkeysState
OldSnapshotControlData
OldSnapshotTimeMapping
OldToNewMapping
OldToNewMappingData
OnCommitAction