tableam: Provide helper functions for relation sizing.
Most block-based table AMs will need the exact same implementation of the relation_size callback as the heap, and if they use a standard page layout, they will likely need an implementation of the relation_estimate_size callback that is very similar to that of the heap. Rearrange to facilitate code reuse. Patch by me, reviewed by Michael Paquier, Daniel Gustafsson, and Álvaro Herrera. Discussion: http://postgr.es/m/CA+TgmoZ6DBPnP1E-vRpQZUJQijJFD54F+SR_pxGiAAS-MyrigA@mail.gmail.com
This commit is contained in:
Robert Haas
parent
482501d433
commit
554106b116
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@ -19,8 +19,6 @@
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*/
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#include "postgres.h"
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#include <math.h>
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#include "miscadmin.h"
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#include "access/genam.h"
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@ -37,7 +35,6 @@
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#include "catalog/storage_xlog.h"
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#include "commands/progress.h"
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#include "executor/executor.h"
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#include "optimizer/plancat.h"
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#include "pgstat.h"
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#include "storage/bufmgr.h"
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#include "storage/bufpage.h"
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@ -1991,26 +1988,6 @@ heapam_scan_get_blocks_done(HeapScanDesc hscan)
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* ------------------------------------------------------------------------
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*/
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static uint64
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heapam_relation_size(Relation rel, ForkNumber forkNumber)
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{
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uint64 nblocks = 0;
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/* Open it at the smgr level if not already done */
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RelationOpenSmgr(rel);
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/* InvalidForkNumber indicates returning the size for all forks */
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if (forkNumber == InvalidForkNumber)
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{
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for (int i = 0; i < MAX_FORKNUM; i++)
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nblocks += smgrnblocks(rel->rd_smgr, i);
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}
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else
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nblocks = smgrnblocks(rel->rd_smgr, forkNumber);
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return nblocks * BLCKSZ;
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}
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/*
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* Check to see whether the table needs a TOAST table. It does only if
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* (1) there are any toastable attributes, and (2) the maximum length
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@ -2068,106 +2045,20 @@ heapam_relation_needs_toast_table(Relation rel)
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* ------------------------------------------------------------------------
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*/
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#define HEAP_OVERHEAD_BYTES_PER_TUPLE \
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(MAXALIGN(SizeofHeapTupleHeader) + sizeof(ItemIdData))
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#define HEAP_USABLE_BYTES_PER_PAGE \
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(BLCKSZ - SizeOfPageHeaderData)
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static void
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heapam_estimate_rel_size(Relation rel, int32 *attr_widths,
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BlockNumber *pages, double *tuples,
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double *allvisfrac)
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{
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BlockNumber curpages;
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BlockNumber relpages;
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double reltuples;
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BlockNumber relallvisible;
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double density;
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/* it has storage, ok to call the smgr */
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curpages = RelationGetNumberOfBlocks(rel);
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/* coerce values in pg_class to more desirable types */
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relpages = (BlockNumber) rel->rd_rel->relpages;
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reltuples = (double) rel->rd_rel->reltuples;
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relallvisible = (BlockNumber) rel->rd_rel->relallvisible;
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/*
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* HACK: if the relation has never yet been vacuumed, use a minimum size
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* estimate of 10 pages. The idea here is to avoid assuming a
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* newly-created table is really small, even if it currently is, because
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* that may not be true once some data gets loaded into it. Once a vacuum
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* or analyze cycle has been done on it, it's more reasonable to believe
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* the size is somewhat stable.
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*
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* (Note that this is only an issue if the plan gets cached and used again
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* after the table has been filled. What we're trying to avoid is using a
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* nestloop-type plan on a table that has grown substantially since the
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* plan was made. Normally, autovacuum/autoanalyze will occur once enough
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* inserts have happened and cause cached-plan invalidation; but that
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* doesn't happen instantaneously, and it won't happen at all for cases
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* such as temporary tables.)
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*
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* We approximate "never vacuumed" by "has relpages = 0", which means this
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* will also fire on genuinely empty relations. Not great, but
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* fortunately that's a seldom-seen case in the real world, and it
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* shouldn't degrade the quality of the plan too much anyway to err in
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* this direction.
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*
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* If the table has inheritance children, we don't apply this heuristic.
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* Totally empty parent tables are quite common, so we should be willing
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* to believe that they are empty.
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*/
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if (curpages < 10 &&
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relpages == 0 &&
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!rel->rd_rel->relhassubclass)
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curpages = 10;
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/* report estimated # pages */
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*pages = curpages;
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/* quick exit if rel is clearly empty */
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if (curpages == 0)
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{
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*tuples = 0;
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*allvisfrac = 0;
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return;
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}
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/* estimate number of tuples from previous tuple density */
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if (relpages > 0)
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density = reltuples / (double) relpages;
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else
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{
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/*
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* When we have no data because the relation was truncated, estimate
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* tuple width from attribute datatypes. We assume here that the
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* pages are completely full, which is OK for tables (since they've
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* presumably not been VACUUMed yet) but is probably an overestimate
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* for indexes. Fortunately get_relation_info() can clamp the
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* overestimate to the parent table's size.
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*
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* Note: this code intentionally disregards alignment considerations,
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* because (a) that would be gilding the lily considering how crude
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* the estimate is, and (b) it creates platform dependencies in the
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* default plans which are kind of a headache for regression testing.
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*/
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int32 tuple_width;
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tuple_width = get_rel_data_width(rel, attr_widths);
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tuple_width += MAXALIGN(SizeofHeapTupleHeader);
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tuple_width += sizeof(ItemIdData);
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/* note: integer division is intentional here */
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density = (BLCKSZ - SizeOfPageHeaderData) / tuple_width;
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}
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*tuples = rint(density * (double) curpages);
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/*
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* We use relallvisible as-is, rather than scaling it up like we do for
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* the pages and tuples counts, on the theory that any pages added since
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* the last VACUUM are most likely not marked all-visible. But costsize.c
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* wants it converted to a fraction.
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*/
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if (relallvisible == 0 || curpages <= 0)
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*allvisfrac = 0;
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else if ((double) relallvisible >= curpages)
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*allvisfrac = 1;
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else
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*allvisfrac = (double) relallvisible / curpages;
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table_block_relation_estimate_size(rel, attr_widths, pages,
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tuples, allvisfrac,
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HEAP_OVERHEAD_BYTES_PER_TUPLE,
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HEAP_USABLE_BYTES_PER_PAGE);
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}
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@ -2644,7 +2535,7 @@ static const TableAmRoutine heapam_methods = {
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.index_build_range_scan = heapam_index_build_range_scan,
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.index_validate_scan = heapam_index_validate_scan,
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.relation_size = heapam_relation_size,
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.relation_size = table_block_relation_size,
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.relation_needs_toast_table = heapam_relation_needs_toast_table,
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.relation_estimate_size = heapam_estimate_rel_size,
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@ -19,11 +19,15 @@
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*/
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#include "postgres.h"
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#include <math.h>
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#include "access/heapam.h" /* for ss_* */
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#include "access/tableam.h"
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#include "access/xact.h"
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#include "optimizer/plancat.h"
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#include "storage/bufmgr.h"
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#include "storage/shmem.h"
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#include "storage/smgr.h"
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/* GUC variables */
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@ -486,3 +490,160 @@ table_block_parallelscan_nextpage(Relation rel, ParallelBlockTableScanDesc pbsca
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return page;
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}
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/* ----------------------------------------------------------------------------
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* Helper functions to implement relation sizing for block oriented AMs.
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* ----------------------------------------------------------------------------
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*/
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/*
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* table_block_relation_size
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*
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* If a table AM uses the various relation forks as the sole place where data
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* is stored, and if it uses them in the expected manner (e.g. the actual data
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* is in the main fork rather than some other), it can use this implementation
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* of the relation_size callback rather than implementing its own.
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*/
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uint64
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table_block_relation_size(Relation rel, ForkNumber forkNumber)
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{
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uint64 nblocks = 0;
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/* Open it at the smgr level if not already done */
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RelationOpenSmgr(rel);
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/* InvalidForkNumber indicates returning the size for all forks */
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if (forkNumber == InvalidForkNumber)
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{
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for (int i = 0; i < MAX_FORKNUM; i++)
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nblocks += smgrnblocks(rel->rd_smgr, i);
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}
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else
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nblocks = smgrnblocks(rel->rd_smgr, forkNumber);
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return nblocks * BLCKSZ;
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}
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/*
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* table_block_relation_estimate_size
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*
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* This function can't be directly used as the implementation of the
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* relation_estimate_size callback, because it has a few additional parameters.
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* Instead, it is intended to be used as a helper function; the caller can
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* pass through the arguments to its relation_estimate_size function plus the
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* additional values required here.
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*
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* overhead_bytes_per_tuple should contain the approximate number of bytes
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* of storage required to store a tuple above and beyond what is required for
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* the tuple data proper. Typically, this would include things like the
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* size of the tuple header and item pointer. This is only used for query
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* planning, so a table AM where the value is not constant could choose to
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* pass a "best guess".
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*
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* usable_bytes_per_page should contain the approximate number of bytes per
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* page usable for tuple data, excluding the page header and any anticipated
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* special space.
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*/
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void
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table_block_relation_estimate_size(Relation rel, int32 *attr_widths,
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BlockNumber *pages, double *tuples,
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double *allvisfrac,
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Size overhead_bytes_per_tuple,
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Size usable_bytes_per_page)
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{
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BlockNumber curpages;
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BlockNumber relpages;
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double reltuples;
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BlockNumber relallvisible;
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double density;
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/* it should have storage, so we can call the smgr */
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curpages = RelationGetNumberOfBlocks(rel);
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/* coerce values in pg_class to more desirable types */
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relpages = (BlockNumber) rel->rd_rel->relpages;
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reltuples = (double) rel->rd_rel->reltuples;
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relallvisible = (BlockNumber) rel->rd_rel->relallvisible;
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/*
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* HACK: if the relation has never yet been vacuumed, use a minimum size
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* estimate of 10 pages. The idea here is to avoid assuming a
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* newly-created table is really small, even if it currently is, because
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* that may not be true once some data gets loaded into it. Once a vacuum
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* or analyze cycle has been done on it, it's more reasonable to believe
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* the size is somewhat stable.
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*
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* (Note that this is only an issue if the plan gets cached and used again
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* after the table has been filled. What we're trying to avoid is using a
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* nestloop-type plan on a table that has grown substantially since the
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* plan was made. Normally, autovacuum/autoanalyze will occur once enough
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* inserts have happened and cause cached-plan invalidation; but that
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* doesn't happen instantaneously, and it won't happen at all for cases
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* such as temporary tables.)
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*
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* We approximate "never vacuumed" by "has relpages = 0", which means this
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* will also fire on genuinely empty relations. Not great, but
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* fortunately that's a seldom-seen case in the real world, and it
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* shouldn't degrade the quality of the plan too much anyway to err in
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* this direction.
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*
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* If the table has inheritance children, we don't apply this heuristic.
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* Totally empty parent tables are quite common, so we should be willing
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* to believe that they are empty.
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*/
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if (curpages < 10 &&
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relpages == 0 &&
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!rel->rd_rel->relhassubclass)
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curpages = 10;
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/* report estimated # pages */
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*pages = curpages;
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/* quick exit if rel is clearly empty */
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if (curpages == 0)
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{
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*tuples = 0;
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*allvisfrac = 0;
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return;
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}
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/* estimate number of tuples from previous tuple density */
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if (relpages > 0)
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density = reltuples / (double) relpages;
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else
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{
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/*
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* When we have no data because the relation was truncated, estimate
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* tuple width from attribute datatypes. We assume here that the
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* pages are completely full, which is OK for tables (since they've
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* presumably not been VACUUMed yet) but is probably an overestimate
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* for indexes. Fortunately get_relation_info() can clamp the
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* overestimate to the parent table's size.
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*
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* Note: this code intentionally disregards alignment considerations,
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* because (a) that would be gilding the lily considering how crude
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* the estimate is, (b) it creates platform dependencies in the
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* default plans which are kind of a headache for regression testing,
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* and (c) different table AMs might use different padding schemes.
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*/
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int32 tuple_width;
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tuple_width = get_rel_data_width(rel, attr_widths);
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tuple_width += overhead_bytes_per_tuple;
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/* note: integer division is intentional here */
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density = usable_bytes_per_page / tuple_width;
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}
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*tuples = rint(density * (double) curpages);
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/*
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* We use relallvisible as-is, rather than scaling it up like we do for
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* the pages and tuples counts, on the theory that any pages added since
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* the last VACUUM are most likely not marked all-visible. But costsize.c
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* wants it converted to a fraction.
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*/
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if (relallvisible == 0 || curpages <= 0)
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*allvisfrac = 0;
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else if ((double) relallvisible >= curpages)
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*allvisfrac = 1;
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else
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*allvisfrac = (double) relallvisible / curpages;
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}
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@ -1727,6 +1727,20 @@ extern void table_block_parallelscan_startblock_init(Relation rel,
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ParallelBlockTableScanDesc pbscan);
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/* ----------------------------------------------------------------------------
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* Helper functions to implement relation sizing for block oriented AMs.
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* ----------------------------------------------------------------------------
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*/
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extern uint64 table_block_relation_size(Relation rel, ForkNumber forkNumber);
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extern void table_block_relation_estimate_size(Relation rel,
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int32 *attr_widths,
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BlockNumber *pages,
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double *tuples,
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double *allvisfrac,
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Size overhead_bytes_per_tuple,
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Size usable_bytes_per_page);
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/* ----------------------------------------------------------------------------
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* Functions in tableamapi.c
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* ----------------------------------------------------------------------------
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