pg_visibility: Add pg_truncate_visibility_map function.
This requires some core changes as well so that we can properly WAL-log the truncation. Specifically, it changes the format of the XLOG_SMGR_TRUNCATE WAL record, so bump XLOG_PAGE_MAGIC. Patch by me, reviewed but not fully endorsed by Andres Freund.
This commit is contained in:
Robert Haas
parent
54f5c5150f
commit
71d05a2c7b
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@ -13,5 +13,12 @@ RETURNS SETOF tid
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AS 'MODULE_PATHNAME', 'pg_check_visible'
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LANGUAGE C STRICT;
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CREATE FUNCTION pg_truncate_visibility_map(regclass)
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RETURNS void
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AS 'MODULE_PATHNAME', 'pg_truncate_visibility_map'
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LANGUAGE C STRICT
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PARALLEL UNSAFE; -- let's not make this any more dangerous
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REVOKE ALL ON FUNCTION pg_check_frozen(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_check_visible(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_truncate_visibility_map(regclass) FROM PUBLIC;
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@ -57,6 +57,13 @@ RETURNS SETOF tid
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AS 'MODULE_PATHNAME', 'pg_check_visible'
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LANGUAGE C STRICT;
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-- Truncate the visibility map fork.
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CREATE FUNCTION pg_truncate_visibility_map(regclass)
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RETURNS void
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AS 'MODULE_PATHNAME', 'pg_truncate_visibility_map'
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LANGUAGE C STRICT
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PARALLEL UNSAFE; -- let's not make this any more dangerous
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-- Don't want these to be available to public.
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REVOKE ALL ON FUNCTION pg_visibility_map(regclass, bigint) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_visibility(regclass, bigint) FROM PUBLIC;
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@ -65,3 +72,4 @@ REVOKE ALL ON FUNCTION pg_visibility(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_visibility_map_summary(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_check_frozen(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_check_visible(regclass) FROM PUBLIC;
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REVOKE ALL ON FUNCTION pg_truncate_visibility_map(regclass) FROM PUBLIC;
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@ -11,10 +11,12 @@
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#include "access/htup_details.h"
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#include "access/visibilitymap.h"
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#include "catalog/pg_type.h"
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#include "catalog/storage_xlog.h"
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#include "funcapi.h"
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#include "miscadmin.h"
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#include "storage/bufmgr.h"
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#include "storage/procarray.h"
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#include "storage/smgr.h"
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#include "utils/rel.h"
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PG_MODULE_MAGIC;
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@ -40,6 +42,7 @@ PG_FUNCTION_INFO_V1(pg_visibility_rel);
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PG_FUNCTION_INFO_V1(pg_visibility_map_summary);
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PG_FUNCTION_INFO_V1(pg_check_frozen);
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PG_FUNCTION_INFO_V1(pg_check_visible);
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PG_FUNCTION_INFO_V1(pg_truncate_visibility_map);
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static TupleDesc pg_visibility_tupdesc(bool include_blkno, bool include_pd);
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static vbits *collect_visibility_data(Oid relid, bool include_pd);
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@ -335,6 +338,75 @@ pg_check_visible(PG_FUNCTION_ARGS)
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SRF_RETURN_DONE(funcctx);
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}
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/*
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* Remove the visibility map fork for a relation. If there turn out to be
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* any bugs in the visibility map code that require rebuilding the VM, this
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* provides users with a way to do it that is cleaner than shutting down the
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* server and removing files by hand.
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*
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* This is a cut-down version of RelationTruncate.
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*/
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Datum
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pg_truncate_visibility_map(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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Relation rel;
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rel = relation_open(relid, AccessExclusiveLock);
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if (rel->rd_rel->relkind != RELKIND_RELATION &&
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rel->rd_rel->relkind != RELKIND_MATVIEW &&
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rel->rd_rel->relkind != RELKIND_TOASTVALUE)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("\"%s\" is not a table, materialized view, or TOAST table",
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RelationGetRelationName(rel))));
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RelationOpenSmgr(rel);
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rel->rd_smgr->smgr_vm_nblocks = InvalidBlockNumber;
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visibilitymap_truncate(rel, 0);
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if (RelationNeedsWAL(rel))
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{
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xl_smgr_truncate xlrec;
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xlrec.blkno = 0;
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xlrec.rnode = rel->rd_node;
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xlrec.flags = SMGR_TRUNCATE_VM;
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XLogBeginInsert();
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XLogRegisterData((char *) &xlrec, sizeof(xlrec));
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XLogInsert(RM_SMGR_ID, XLOG_SMGR_TRUNCATE | XLR_SPECIAL_REL_UPDATE);
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}
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/*
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* Release the lock right away, not at commit time.
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*
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* It would be a problem to release the lock prior to commit if this
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* truncate operation sends any transactional invalidation messages. Other
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* backends would potentially be able to lock the relation without
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* processing them in the window of time between when we release the lock
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* here and when we sent the messages at our eventual commit. However,
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* we're currently only sending a non-transactional smgr invalidation,
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* which will have been posted to shared memory immediately from within
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* visibilitymap_truncate. Therefore, there should be no race here.
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*
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* The reason why it's desirable to release the lock early here is because
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* of the possibility that someone will need to use this to blow away many
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* visibility map forks at once. If we can't release the lock until
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* commit time, the transaction doing this will accumulate
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* AccessExclusiveLocks on all of those relations at the same time, which
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* is undesirable. However, if this turns out to be unsafe we may have no
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* choice...
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*/
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relation_close(rel, AccessExclusiveLock);
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/* Nothing to return. */
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PG_RETURN_VOID();
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}
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/*
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* Helper function to construct whichever TupleDesc we need for a particular
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* call.
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@ -9,14 +9,16 @@
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<para>
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The <filename>pg_visibility</> module provides a means for examining the
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visibility map (VM) and page-level visibility information.
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visibility map (VM) and page-level visibility information. It also
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provides functions to check the integrity of the visibility map and to
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force it to be rebuilt.
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</para>
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<para>
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These routines return information about three different bits. The
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all-visible bit in the visibility map indicates that every tuple on
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a given page of a relation is visible to every current transaction. The
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all-frozen bit in the visibility map indicates that every tuple on the
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Three different bits are used to store information about page-level
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visibility. The all-visible bit in the visibility map indicates that every
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tuple on a given page of a relation is visible to every current transaction.
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The all-frozen bit in the visibility map indicates that every tuple on the
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page is frozen; that is, no future vacuum will need to modify the page
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until such time as a tuple is inserted, updated, deleted, or locked on
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that page. The page-level <literal>PD_ALL_VISIBLE</literal> bit has the
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@ -25,7 +27,8 @@
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will normally agree, but the page-level bit can sometimes be set while the
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visibility map bit is clear after a crash recovery; or they can disagree
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because of a change which occurs after <literal>pg_visibility</> examines
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the visibility map and before it examines the data page.
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the visibility map and before it examines the data page. Any event which
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causes data corruption can also cause these bits to disagree.
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</para>
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<para>
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@ -118,6 +121,21 @@
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><function>pg_truncate_visibility_map(regclass) returns void</function></term>
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<listitem>
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<para>
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Truncates the visibility map for the given relation. This function
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is only expected to be useful if you suspect that the visibility map
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for the indicated relation is corrupt and wish to rebuild it. The first
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<command>VACUUM</> executed on the given relation after this function
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is executed will scan every page in the relation and rebuild the
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visibility map.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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@ -37,7 +37,8 @@ smgr_desc(StringInfo buf, XLogReaderState *record)
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xl_smgr_truncate *xlrec = (xl_smgr_truncate *) rec;
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char *path = relpathperm(xlrec->rnode, MAIN_FORKNUM);
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appendStringInfo(buf, "%s to %u blocks", path, xlrec->blkno);
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appendStringInfo(buf, "%s to %u blocks flags %d", path,
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xlrec->blkno, xlrec->flags);
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pfree(path);
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}
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}
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@ -268,6 +268,7 @@ RelationTruncate(Relation rel, BlockNumber nblocks)
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xlrec.blkno = nblocks;
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xlrec.rnode = rel->rd_node;
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xlrec.flags = SMGR_TRUNCATE_ALL;
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XLogBeginInsert();
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XLogRegisterData((char *) &xlrec, sizeof(xlrec));
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@ -522,17 +523,22 @@ smgr_redo(XLogReaderState *record)
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*/
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XLogFlush(lsn);
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smgrtruncate(reln, MAIN_FORKNUM, xlrec->blkno);
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if ((xlrec->flags & SMGR_TRUNCATE_HEAP) != 0)
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{
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smgrtruncate(reln, MAIN_FORKNUM, xlrec->blkno);
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/* Also tell xlogutils.c about it */
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XLogTruncateRelation(xlrec->rnode, MAIN_FORKNUM, xlrec->blkno);
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/* Also tell xlogutils.c about it */
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XLogTruncateRelation(xlrec->rnode, MAIN_FORKNUM, xlrec->blkno);
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}
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/* Truncate FSM and VM too */
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rel = CreateFakeRelcacheEntry(xlrec->rnode);
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if (smgrexists(reln, FSM_FORKNUM))
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if ((xlrec->flags & SMGR_TRUNCATE_FSM) != 0 &&
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smgrexists(reln, FSM_FORKNUM))
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FreeSpaceMapTruncateRel(rel, xlrec->blkno);
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if (smgrexists(reln, VISIBILITYMAP_FORKNUM))
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if ((xlrec->flags & SMGR_TRUNCATE_VM) != 0 &&
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smgrexists(reln, VISIBILITYMAP_FORKNUM))
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visibilitymap_truncate(rel, xlrec->blkno);
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FreeFakeRelcacheEntry(rel);
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@ -31,7 +31,7 @@
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/*
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* Each page of XLOG file has a header like this:
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*/
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#define XLOG_PAGE_MAGIC 0xD091 /* can be used as WAL version indicator */
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#define XLOG_PAGE_MAGIC 0xD092 /* can be used as WAL version indicator */
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typedef struct XLogPageHeaderData
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{
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@ -36,10 +36,18 @@ typedef struct xl_smgr_create
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ForkNumber forkNum;
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} xl_smgr_create;
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/* flags for xl_smgr_truncate */
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#define SMGR_TRUNCATE_HEAP 0x0001
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#define SMGR_TRUNCATE_VM 0x0002
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#define SMGR_TRUNCATE_FSM 0x0004
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#define SMGR_TRUNCATE_ALL \
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(SMGR_TRUNCATE_HEAP|SMGR_TRUNCATE_VM|SMGR_TRUNCATE_FSM)
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typedef struct xl_smgr_truncate
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{
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BlockNumber blkno;
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RelFileNode rnode;
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int flags;
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} xl_smgr_truncate;
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extern void log_smgrcreate(RelFileNode *rnode, ForkNumber forkNum);
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