Add pg_visibility contrib module.
This lets you examine the visibility map as well as page-level visibility information. I initially wrote it as a debugging aid, but was encouraged to polish it for commit. Patch by me, reviewed by Masahiko Sawada. Discussion: 56D77803.6080503@BlueTreble.com
This commit is contained in:
Robert Haas
parent
6f56b41ac0
commit
ba0a198fb1
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@ -37,6 +37,7 @@ SUBDIRS = \
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pgcrypto \
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pgrowlocks \
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pgstattuple \
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pg_visibility \
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postgres_fdw \
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seg \
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spi \
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@ -0,0 +1,19 @@
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# contrib/pg_visibility/Makefile
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MODULE_big = pg_visibility
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OBJS = pg_visibility.o $(WIN32RES)
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EXTENSION = pg_visibility
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DATA = pg_visibility--1.0.sql
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PGFILEDESC = "pg_visibility - page visibility information"
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = contrib/pg_visibility
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif
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@ -0,0 +1,52 @@
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/* contrib/pg_visibility/pg_visibility--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION pg_visibility" to load this file. \quit
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-- Show visibility map information.
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CREATE FUNCTION pg_visibility_map(regclass, blkno bigint,
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all_visible OUT boolean,
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all_frozen OUT boolean)
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RETURNS record
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AS 'MODULE_PATHNAME', 'pg_visibility_map'
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LANGUAGE C STRICT;
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-- Show visibility map and page-level visibility information.
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CREATE FUNCTION pg_visibility(regclass, blkno bigint,
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all_visible OUT boolean,
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all_frozen OUT boolean,
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pd_all_visible OUT boolean)
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RETURNS record
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AS 'MODULE_PATHNAME', 'pg_visibility'
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LANGUAGE C STRICT;
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-- Show visibility map information for each block in a relation.
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CREATE FUNCTION pg_visibility_map(regclass, blkno OUT bigint,
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all_visible OUT boolean,
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all_frozen OUT boolean)
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RETURNS SETOF record
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AS 'MODULE_PATHNAME', 'pg_visibility_map_rel'
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LANGUAGE C STRICT;
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-- Show visibility map and page-level visibility information for each block.
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CREATE FUNCTION pg_visibility(regclass, blkno OUT bigint,
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all_visible OUT boolean,
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all_frozen OUT boolean,
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pd_all_visible OUT boolean)
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RETURNS SETOF record
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AS 'MODULE_PATHNAME', 'pg_visibility_rel'
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LANGUAGE C STRICT;
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-- Show summary of visibility map bits for a relation.
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CREATE FUNCTION pg_visibility_map_summary(regclass,
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OUT all_visible bigint, OUT all_frozen bigint)
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RETURNS record
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AS 'MODULE_PATHNAME', 'pg_visibility_map_summary'
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LANGUAGE C STRICT;
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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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REVOKE ALL ON FUNCTION pg_visibility_map(regclass) FROM PUBLIC;
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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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@ -0,0 +1,350 @@
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/*-------------------------------------------------------------------------
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*
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* pg_visibility.c
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* display visibility map information and page-level visibility bits
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*
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* contrib/pg_visibility/pg_visibility.c
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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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 "funcapi.h"
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#include "miscadmin.h"
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#include "storage/bufmgr.h"
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#include "utils/rel.h"
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PG_MODULE_MAGIC;
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typedef struct vbits
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{
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BlockNumber next;
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BlockNumber count;
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uint8 bits[FLEXIBLE_ARRAY_MEMBER];
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} vbits;
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PG_FUNCTION_INFO_V1(pg_visibility_map);
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PG_FUNCTION_INFO_V1(pg_visibility_map_rel);
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PG_FUNCTION_INFO_V1(pg_visibility);
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PG_FUNCTION_INFO_V1(pg_visibility_rel);
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PG_FUNCTION_INFO_V1(pg_visibility_map_summary);
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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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/*
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* Visibility map information for a single block of a relation.
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*/
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Datum
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pg_visibility_map(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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int64 blkno = PG_GETARG_INT64(1);
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int32 mapbits;
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Relation rel;
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Buffer vmbuffer = InvalidBuffer;
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TupleDesc tupdesc;
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Datum values[2];
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bool nulls[2];
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rel = relation_open(relid, AccessShareLock);
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if (blkno < 0 || blkno > MaxBlockNumber)
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("invalid block number")));
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tupdesc = pg_visibility_tupdesc(false, false);
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MemSet(nulls, 0, sizeof(nulls));
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mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
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if (vmbuffer != InvalidBuffer)
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ReleaseBuffer(vmbuffer);
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values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
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values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
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relation_close(rel, AccessShareLock);
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PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
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}
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/*
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* Visibility map information for a single block of a relation, plus the
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* page-level information for the same block.
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*/
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Datum
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pg_visibility(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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int64 blkno = PG_GETARG_INT64(1);
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int32 mapbits;
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Relation rel;
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Buffer vmbuffer = InvalidBuffer;
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Buffer buffer;
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Page page;
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TupleDesc tupdesc;
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Datum values[3];
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bool nulls[3];
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rel = relation_open(relid, AccessShareLock);
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if (blkno < 0 || blkno > MaxBlockNumber)
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("invalid block number")));
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tupdesc = pg_visibility_tupdesc(false, true);
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MemSet(nulls, 0, sizeof(nulls));
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mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
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if (vmbuffer != InvalidBuffer)
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ReleaseBuffer(vmbuffer);
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values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
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values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
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buffer = ReadBuffer(rel, blkno);
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LockBuffer(buffer, BUFFER_LOCK_SHARE);
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page = BufferGetPage(buffer);
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values[2] = BoolGetDatum(PageIsAllVisible(page));
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UnlockReleaseBuffer(buffer);
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relation_close(rel, AccessShareLock);
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PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
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}
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/*
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* Visibility map information for every block in a relation.
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*/
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Datum
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pg_visibility_map_rel(PG_FUNCTION_ARGS)
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{
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FuncCallContext *funcctx;
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vbits *info;
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if (SRF_IS_FIRSTCALL())
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{
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Oid relid = PG_GETARG_OID(0);
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MemoryContext oldcontext;
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funcctx = SRF_FIRSTCALL_INIT();
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oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
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funcctx->tuple_desc = pg_visibility_tupdesc(true, false);
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funcctx->user_fctx = collect_visibility_data(relid, false);
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MemoryContextSwitchTo(oldcontext);
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}
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funcctx = SRF_PERCALL_SETUP();
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info = (vbits *) funcctx->user_fctx;
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if (info->next < info->count)
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{
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Datum values[3];
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bool nulls[3];
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HeapTuple tuple;
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MemSet(nulls, 0, sizeof(nulls));
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values[0] = Int64GetDatum(info->next);
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values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
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values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
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info->next++;
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tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
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SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
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}
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SRF_RETURN_DONE(funcctx);
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}
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/*
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* Visibility map information for every block in a relation, plus the page
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* level information for each block.
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*/
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Datum
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pg_visibility_rel(PG_FUNCTION_ARGS)
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{
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FuncCallContext *funcctx;
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vbits *info;
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if (SRF_IS_FIRSTCALL())
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{
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Oid relid = PG_GETARG_OID(0);
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MemoryContext oldcontext;
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funcctx = SRF_FIRSTCALL_INIT();
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oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
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funcctx->tuple_desc = pg_visibility_tupdesc(true, true);
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funcctx->user_fctx = collect_visibility_data(relid, true);
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MemoryContextSwitchTo(oldcontext);
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}
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funcctx = SRF_PERCALL_SETUP();
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info = (vbits *) funcctx->user_fctx;
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if (info->next < info->count)
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{
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Datum values[4];
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bool nulls[4];
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HeapTuple tuple;
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MemSet(nulls, 0, sizeof(nulls));
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values[0] = Int64GetDatum(info->next);
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values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
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values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
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values[3] = BoolGetDatum((info->bits[info->next] & (1 << 2)) != 0);
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info->next++;
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tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
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SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
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}
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SRF_RETURN_DONE(funcctx);
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}
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/*
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* Count the number of all-visible and all-frozen pages in the visibility
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* map for a particular relation.
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*/
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Datum
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pg_visibility_map_summary(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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BlockNumber nblocks;
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BlockNumber blkno;
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Buffer vmbuffer = InvalidBuffer;
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int64 all_visible = 0;
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int64 all_frozen = 0;
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TupleDesc tupdesc;
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Datum values[2];
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bool nulls[2];
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rel = relation_open(relid, AccessShareLock);
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nblocks = RelationGetNumberOfBlocks(rel);
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for (blkno = 0; blkno < nblocks; ++blkno)
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{
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int32 mapbits;
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/* Make sure we are interruptible. */
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CHECK_FOR_INTERRUPTS();
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/* Get map info. */
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mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
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if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
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++all_visible;
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if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
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++all_frozen;
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}
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/* Clean up. */
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if (vmbuffer != InvalidBuffer)
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ReleaseBuffer(vmbuffer);
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relation_close(rel, AccessShareLock);
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tupdesc = CreateTemplateTupleDesc(2, false);
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TupleDescInitEntry(tupdesc, (AttrNumber) 1, "all_visible", INT8OID, -1, 0);
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TupleDescInitEntry(tupdesc, (AttrNumber) 2, "all_frozen", INT8OID, -1, 0);
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tupdesc = BlessTupleDesc(tupdesc);
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MemSet(nulls, 0, sizeof(nulls));
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values[0] = Int64GetDatum(all_visible);
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values[1] = Int64GetDatum(all_frozen);
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PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
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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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*/
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static TupleDesc
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pg_visibility_tupdesc(bool include_blkno, bool include_pd)
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{
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TupleDesc tupdesc;
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AttrNumber maxattr = 2;
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AttrNumber a = 0;
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if (include_blkno)
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++maxattr;
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if (include_pd)
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++maxattr;
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tupdesc = CreateTemplateTupleDesc(maxattr, false);
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if (include_blkno)
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TupleDescInitEntry(tupdesc, ++a, "blkno", INT8OID, -1, 0);
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TupleDescInitEntry(tupdesc, ++a, "all_visible", BOOLOID, -1, 0);
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TupleDescInitEntry(tupdesc, ++a, "all_frozen", BOOLOID, -1, 0);
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if (include_pd)
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TupleDescInitEntry(tupdesc, ++a, "pd_all_visible", BOOLOID, -1, 0);
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Assert(a == maxattr);
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return BlessTupleDesc(tupdesc);
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}
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/*
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* Collect visibility data about a relation.
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*/
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static vbits *
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collect_visibility_data(Oid relid, bool include_pd)
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{
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Relation rel;
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BlockNumber nblocks;
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vbits *info;
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BlockNumber blkno;
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Buffer vmbuffer = InvalidBuffer;
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BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
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rel = relation_open(relid, AccessShareLock);
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nblocks = RelationGetNumberOfBlocks(rel);
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info = palloc0(offsetof(vbits, bits) + nblocks);
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info->next = 0;
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info->count = nblocks;
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for (blkno = 0; blkno < nblocks; ++blkno)
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{
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int32 mapbits;
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/* Make sure we are interruptible. */
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CHECK_FOR_INTERRUPTS();
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/* Get map info. */
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mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
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if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
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info->bits[blkno] |= (1 << 0);
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if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
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info->bits[blkno] |= (1 << 1);
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/*
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* Page-level data requires reading every block, so only get it if
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* the caller needs it. Use a buffer access strategy, too, to prevent
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* cache-trashing.
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*/
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if (include_pd)
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{
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Buffer buffer;
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Page page;
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buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
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bstrategy);
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LockBuffer(buffer, BUFFER_LOCK_SHARE);
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page = BufferGetPage(buffer);
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if (PageIsAllVisible(page))
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info->bits[blkno] |= (1 << 2);
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UnlockReleaseBuffer(buffer);
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}
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}
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/* Clean up. */
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if (vmbuffer != InvalidBuffer)
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ReleaseBuffer(vmbuffer);
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relation_close(rel, AccessShareLock);
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return info;
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}
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@ -0,0 +1,5 @@
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# pg_visibility extension
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comment = 'examine the visibility map (VM) and page-level visibility info'
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default_version = '1.0'
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module_pathname = '$libdir/pg_visibility'
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relocatable = true
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@ -132,6 +132,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
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&pgstatstatements;
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&pgstattuple;
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&pgtrgm;
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&pgvisibility;
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&postgres-fdw;
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&seg;
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&sepgsql;
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@ -136,6 +136,7 @@
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<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">
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<!ENTITY pgstattuple SYSTEM "pgstattuple.sgml">
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<!ENTITY pgtrgm SYSTEM "pgtrgm.sgml">
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<!ENTITY pgvisibility SYSTEM "pgvisibility.sgml">
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<!ENTITY postgres-fdw SYSTEM "postgres-fdw.sgml">
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<!ENTITY seg SYSTEM "seg.sgml">
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<!ENTITY contrib-spi SYSTEM "contrib-spi.sgml">
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@ -0,0 +1,110 @@
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<!-- doc/src/sgml/pgvisibility.sgml -->
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<sect1 id="pgvisibility" xreflabel="pg_visibility">
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<title>pg_visibility</title>
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<indexterm zone="pgvisibility">
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<primary>pg_visibility</primary>
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</indexterm>
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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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</para>
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|
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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
|
||||
a given page of a relation is visible to every current transaction. The
|
||||
all-frozen bit in the visibility map indicates that every tuple on the
|
||||
page is frozen; that is, no future vacuum will need to modify the page
|
||||
until such time as a tuple is inserted, updated, deleted, or locked on
|
||||
that page. The page-level <literal>PD_ALL_VISIBLE</literal> bit has the
|
||||
same meaning as the all-visible bit in the visibility map, but is stored
|
||||
within the data page itself rather than a separate data tructure. These
|
||||
will normally agree, but the page-level bit can sometimes be set while the
|
||||
visibility map bit is clear after a crash recovery; or they can disagree
|
||||
because of a change which occurs after <literal>pg_visibility</> examines
|
||||
the visibility map and before it examines the data page.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
Functions which display information about <literal>PG_ALL_VISIBLE</>
|
||||
are much more costly than those which only consult the visibility map,
|
||||
because they must read the relation's data blocks rather than only the
|
||||
(much smaller) visibility map.
|
||||
</para>
|
||||
|
||||
<sect2>
|
||||
<title>Functions</title>
|
||||
|
||||
<variablelist>
|
||||
<varlistentry>
|
||||
<term><function>pg_visibility_map(regclass, blkno bigint, all_visible OUT boolean, all_frozen OUT boolean) returns record</function></term>
|
||||
<listitem>
|
||||
<para>
|
||||
Returns the all-visible and all-frozen bits in the visibility map for
|
||||
the given block of the given relation.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><function>pg_visibility(regclass, blkno bigint, all_visible OUT boolean, all_frozen OUT boolean, pd_all_visible OUT boolean) returns record</function></term>
|
||||
<listitem>
|
||||
<para>
|
||||
Returns the all-visible and all-frozen bits in the visibility map for
|
||||
the given block of the given relation, plus the
|
||||
<literal>PD_ALL_VISIBILE</> bit for that block.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><function>pg_visibility_map(regclass, blkno OUT bigint, all_visible OUT boolean, all_frozen OUT boolean) returns record</function></term>
|
||||
<listitem>
|
||||
<para>
|
||||
Returns the all-visible and all-frozen bits in the visibility map for
|
||||
each block the given relation.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><function>pg_visibility(regclass, blkno OUT bigint, all_visible OUT boolean, all_frozen OUT boolean, pd_all_visible OUT boolean) returns record</function></term>
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
Returns the all-visible and all-frozen bits in the visibility map for
|
||||
each block the given relation, plus the <literal>PD_ALL_VISIBLE</>
|
||||
bit for each block.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><function>pg_visibility_map_summary(regclass, all_visible OUT bigint, all_frozen OUT bigint) returns record</function></term>
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
Returns the number of all-visible pages and the number of all-frozen
|
||||
pages in the relation according to the visibility map.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
</variablelist>
|
||||
|
||||
<para>
|
||||
By default, these functions are not publicly executable.
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
<sect2>
|
||||
<title>Author</title>
|
||||
|
||||
<para>
|
||||
Robert Haas <email>rhaas@postgresql.org</email>
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
</sect1>
|
||||
|
|
@ -648,6 +648,11 @@ might not be true. Visibility map bits are only set by vacuum, but are
|
|||
cleared by any data-modifying operations on a page.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
The <xref linkend="pgvisibility"> module can be used to examine the
|
||||
information stored in the visibility map.
|
||||
</para>
|
||||
|
||||
</sect1>
|
||||
|
||||
<sect1 id="storage-init">
|
||||
|
|
|
|||
Loading…
Reference in New Issue