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Add pg_visibility contrib module.

Browse Source 
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
pull/11/head
Robert Haas 10 years ago
parent 6f56b41ac0
commit ba0a198fb1
9 changed files with 544 additions and 0 deletions
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  1. 1
      contrib/Makefile
  2. 19
      contrib/pg_visibility/Makefile
  3. 52
      contrib/pg_visibility/pg_visibility--1.0.sql
  4. 350
      contrib/pg_visibility/pg_visibility.c
  5. 5
      contrib/pg_visibility/pg_visibility.control
  6. 1
      doc/src/sgml/contrib.sgml
  7. 1
      doc/src/sgml/filelist.sgml
  8. 110
      doc/src/sgml/pgvisibility.sgml
  9. 5
      doc/src/sgml/storage.sgml

1
contrib/Makefile
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@ -37,6 +37,7 @@ SUBDIRS = \
pgcrypto \
pgrowlocks \
pgstattuple \
pg_visibility \
postgres_fdw \
seg \
spi \

19
contrib/pg_visibility/Makefile
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@ -0,0 +1,19 @@
# contrib/pg_visibility/Makefile
MODULE_big = pg_visibility
OBJS = pg_visibility.o $(WIN32RES)
EXTENSION = pg_visibility
DATA = pg_visibility--1.0.sql
PGFILEDESC = "pg_visibility - page visibility information"
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/pg_visibility
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

52
contrib/pg_visibility/pg_visibility--1.0.sql
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/* contrib/pg_visibility/pg_visibility--1.0.sql */
-- complain if script is sourced in psql, rather than via CREATE EXTENSION
\echo Use "CREATE EXTENSION pg_visibility" to load this file. \quit
-- Show visibility map information.
CREATE FUNCTION pg_visibility_map(regclass, blkno bigint,
all_visible OUT boolean,
all_frozen OUT boolean)
RETURNS record
AS 'MODULE_PATHNAME', 'pg_visibility_map'
LANGUAGE C STRICT;
-- Show visibility map and page-level visibility information.
CREATE FUNCTION pg_visibility(regclass, blkno bigint,
all_visible OUT boolean,
all_frozen OUT boolean,
pd_all_visible OUT boolean)
RETURNS record
AS 'MODULE_PATHNAME', 'pg_visibility'
LANGUAGE C STRICT;
-- Show visibility map information for each block in a relation.
CREATE FUNCTION pg_visibility_map(regclass, blkno OUT bigint,
all_visible OUT boolean,
all_frozen OUT boolean)
RETURNS SETOF record
AS 'MODULE_PATHNAME', 'pg_visibility_map_rel'
LANGUAGE C STRICT;
-- Show visibility map and page-level visibility information for each block.
CREATE FUNCTION pg_visibility(regclass, blkno OUT bigint,
all_visible OUT boolean,
all_frozen OUT boolean,
pd_all_visible OUT boolean)
RETURNS SETOF record
AS 'MODULE_PATHNAME', 'pg_visibility_rel'
LANGUAGE C STRICT;
-- Show summary of visibility map bits for a relation.
CREATE FUNCTION pg_visibility_map_summary(regclass,
OUT all_visible bigint, OUT all_frozen bigint)
RETURNS record
AS 'MODULE_PATHNAME', 'pg_visibility_map_summary'
LANGUAGE C STRICT;
-- Don't want these to be available to public.
REVOKE ALL ON FUNCTION pg_visibility_map(regclass, bigint) FROM PUBLIC;
REVOKE ALL ON FUNCTION pg_visibility(regclass, bigint) FROM PUBLIC;
REVOKE ALL ON FUNCTION pg_visibility_map(regclass) FROM PUBLIC;
REVOKE ALL ON FUNCTION pg_visibility(regclass) FROM PUBLIC;
REVOKE ALL ON FUNCTION pg_visibility_map_summary(regclass) FROM PUBLIC;

350
contrib/pg_visibility/pg_visibility.c
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@ -0,0 +1,350 @@
/*-------------------------------------------------------------------------
*
* pg_visibility.c
* display visibility map information and page-level visibility bits
*
* contrib/pg_visibility/pg_visibility.c
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/visibilitymap.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "utils/rel.h"
PG_MODULE_MAGIC;
typedef struct vbits
{
BlockNumber next;
BlockNumber count;
uint8 bits[FLEXIBLE_ARRAY_MEMBER];
} vbits;
PG_FUNCTION_INFO_V1(pg_visibility_map);
PG_FUNCTION_INFO_V1(pg_visibility_map_rel);
PG_FUNCTION_INFO_V1(pg_visibility);
PG_FUNCTION_INFO_V1(pg_visibility_rel);
PG_FUNCTION_INFO_V1(pg_visibility_map_summary);
static TupleDesc pg_visibility_tupdesc(bool include_blkno, bool include_pd);
static vbits *collect_visibility_data(Oid relid, bool include_pd);
/*
* Visibility map information for a single block of a relation.
*/
Datum
pg_visibility_map(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
int64 blkno = PG_GETARG_INT64(1);
int32 mapbits;
Relation rel;
Buffer vmbuffer = InvalidBuffer;
TupleDesc tupdesc;
Datum values[2];
bool nulls[2];
rel = relation_open(relid, AccessShareLock);
if (blkno < 0 || blkno > MaxBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid block number")));
tupdesc = pg_visibility_tupdesc(false, false);
MemSet(nulls, 0, sizeof(nulls));
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
relation_close(rel, AccessShareLock);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Visibility map information for a single block of a relation, plus the
* page-level information for the same block.
*/
Datum
pg_visibility(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
int64 blkno = PG_GETARG_INT64(1);
int32 mapbits;
Relation rel;
Buffer vmbuffer = InvalidBuffer;
Buffer buffer;
Page page;
TupleDesc tupdesc;
Datum values[3];
bool nulls[3];
rel = relation_open(relid, AccessShareLock);
if (blkno < 0 || blkno > MaxBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid block number")));
tupdesc = pg_visibility_tupdesc(false, true);
MemSet(nulls, 0, sizeof(nulls));
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
buffer = ReadBuffer(rel, blkno);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
values[2] = BoolGetDatum(PageIsAllVisible(page));
UnlockReleaseBuffer(buffer);
relation_close(rel, AccessShareLock);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Visibility map information for every block in a relation.
*/
Datum
pg_visibility_map_rel(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
vbits *info;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
funcctx->tuple_desc = pg_visibility_tupdesc(true, false);
funcctx->user_fctx = collect_visibility_data(relid, false);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
info = (vbits *) funcctx->user_fctx;
if (info->next < info->count)
{
Datum values[3];
bool nulls[3];
HeapTuple tuple;
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(info->next);
values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
info->next++;
tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
SRF_RETURN_DONE(funcctx);
}
/*
* Visibility map information for every block in a relation, plus the page
* level information for each block.
*/
Datum
pg_visibility_rel(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
vbits *info;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
funcctx->tuple_desc = pg_visibility_tupdesc(true, true);
funcctx->user_fctx = collect_visibility_data(relid, true);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
info = (vbits *) funcctx->user_fctx;
if (info->next < info->count)
{
Datum values[4];
bool nulls[4];
HeapTuple tuple;
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(info->next);
values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
values[3] = BoolGetDatum((info->bits[info->next] & (1 << 2)) != 0);
info->next++;
tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
SRF_RETURN_DONE(funcctx);
}
/*
* Count the number of all-visible and all-frozen pages in the visibility
* map for a particular relation.
*/
Datum
pg_visibility_map_summary(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
Relation rel;
BlockNumber nblocks;
BlockNumber blkno;
Buffer vmbuffer = InvalidBuffer;
int64 all_visible = 0;
int64 all_frozen = 0;
TupleDesc tupdesc;
Datum values[2];
bool nulls[2];
rel = relation_open(relid, AccessShareLock);
nblocks = RelationGetNumberOfBlocks(rel);
for (blkno = 0; blkno < nblocks; ++blkno)
{
int32 mapbits;
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
/* Get map info. */
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
++all_visible;
if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
++all_frozen;
}
/* Clean up. */
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
relation_close(rel, AccessShareLock);
tupdesc = CreateTemplateTupleDesc(2, false);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "all_visible", INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "all_frozen", INT8OID, -1, 0);
tupdesc = BlessTupleDesc(tupdesc);
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(all_visible);
values[1] = Int64GetDatum(all_frozen);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Helper function to construct whichever TupleDesc we need for a particular
* call.
*/
static TupleDesc
pg_visibility_tupdesc(bool include_blkno, bool include_pd)
{
TupleDesc tupdesc;
AttrNumber maxattr = 2;
AttrNumber a = 0;
if (include_blkno)
++maxattr;
if (include_pd)
++maxattr;
tupdesc = CreateTemplateTupleDesc(maxattr, false);
if (include_blkno)
TupleDescInitEntry(tupdesc, ++a, "blkno", INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, ++a, "all_visible", BOOLOID, -1, 0);
TupleDescInitEntry(tupdesc, ++a, "all_frozen", BOOLOID, -1, 0);
if (include_pd)
TupleDescInitEntry(tupdesc, ++a, "pd_all_visible", BOOLOID, -1, 0);
Assert(a == maxattr);
return BlessTupleDesc(tupdesc);
}
/*
* Collect visibility data about a relation.
*/
static vbits *
collect_visibility_data(Oid relid, bool include_pd)
{
Relation rel;
BlockNumber nblocks;
vbits *info;
BlockNumber blkno;
Buffer vmbuffer = InvalidBuffer;
BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
rel = relation_open(relid, AccessShareLock);
nblocks = RelationGetNumberOfBlocks(rel);
info = palloc0(offsetof(vbits, bits) + nblocks);
info->next = 0;
info->count = nblocks;
for (blkno = 0; blkno < nblocks; ++blkno)
{
int32 mapbits;
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
/* Get map info. */
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
info->bits[blkno] |= (1 << 0);
if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
info->bits[blkno] |= (1 << 1);
/*
* Page-level data requires reading every block, so only get it if
* the caller needs it. Use a buffer access strategy, too, to prevent
* cache-trashing.
*/
if (include_pd)
{
Buffer buffer;
Page page;
buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
bstrategy);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
if (PageIsAllVisible(page))
info->bits[blkno] |= (1 << 2);
UnlockReleaseBuffer(buffer);
}
}
/* Clean up. */
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
relation_close(rel, AccessShareLock);
return info;
}

5
contrib/pg_visibility/pg_visibility.control
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@ -0,0 +1,5 @@
# pg_visibility extension
comment = 'examine the visibility map (VM) and page-level visibility info'
default_version = '1.0'
module_pathname = '$libdir/pg_visibility'
relocatable = true

1
doc/src/sgml/contrib.sgml
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@ -132,6 +132,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
&pgstatstatements;
&pgstattuple;
&pgtrgm;
&pgvisibility;
&postgres-fdw;
&seg;
&sepgsql;

1
doc/src/sgml/filelist.sgml
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@ -136,6 +136,7 @@
<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">
<!ENTITY pgstattuple SYSTEM "pgstattuple.sgml">
<!ENTITY pgtrgm SYSTEM "pgtrgm.sgml">
<!ENTITY pgvisibility SYSTEM "pgvisibility.sgml">
<!ENTITY postgres-fdw SYSTEM "postgres-fdw.sgml">
<!ENTITY seg SYSTEM "seg.sgml">
<!ENTITY contrib-spi SYSTEM "contrib-spi.sgml">

110
doc/src/sgml/pgvisibility.sgml
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<!-- doc/src/sgml/pgvisibility.sgml -->
<sect1 id="pgvisibility" xreflabel="pg_visibility">
<title>pg_visibility</title>
<indexterm zone="pgvisibility">
<primary>pg_visibility</primary>
</indexterm>
<para>
The <filename>pg_visibility</> module provides a means for examining the
visibility map (VM) and page-level visibility information.
</para>
<para>
These routines return information about three different bits. The
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>

5
doc/src/sgml/storage.sgml
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@ -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">

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