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robertmhaasrobertmhaas
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pg_prewarm, a contrib module for prewarming relationd data.
Patch by me. Review by Álvaro Herrera, Amit Kapila, Jeff Janes, Gurjeet Singh, and others.
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‎contrib/Makefile

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@@ -32,6 +32,7 @@ SUBDIRS = \
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pg_archivecleanup \
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pg_buffercache \
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pg_freespacemap \
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pg_prewarm \
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pg_standby \
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pg_stat_statements \
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pg_test_fsync \

‎contrib/pg_prewarm/Makefile

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# contrib/pg_prewarm/Makefile
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MODULE_big = pg_prewarm
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OBJS = pg_prewarm.o
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EXTENSION = pg_prewarm
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DATA = pg_prewarm--1.0.sql
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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_prewarm
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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

‎contrib/pg_prewarm/pg_prewarm--1.0.sql

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/* contrib/pg_prewarm/pg_prewarm--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_prewarm" to load this file. \quit
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-- Register the function.
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CREATE FUNCTION pg_prewarm(regclass,
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mode text default 'buffer',
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fork text default 'main',
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first_block int8 default null,
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last_block int8 default null)
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RETURNS int8
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AS 'MODULE_PATHNAME', 'pg_prewarm'
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LANGUAGE C;

‎contrib/pg_prewarm/pg_prewarm.c

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/*-------------------------------------------------------------------------
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*
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* pg_prewarm.c
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* prewarming utilities
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*
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* Copyright (c) 2010-2013, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/pg_prewarm/pg_prewarm.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <sys/stat.h>
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#include <unistd.h>
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#include "access/heapam.h"
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#include "catalog/catalog.h"
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#include "fmgr.h"
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#include "miscadmin.h"
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#include "storage/bufmgr.h"
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#include "storage/smgr.h"
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#include "utils/acl.h"
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#include "utils/builtins.h"
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#include "utils/lsyscache.h"
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#include "utils/rel.h"
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PG_MODULE_MAGIC;
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extern Datum pg_prewarm(PG_FUNCTION_ARGS);
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PG_FUNCTION_INFO_V1(pg_prewarm);
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typedef enum
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{
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PREWARM_PREFETCH,
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PREWARM_READ,
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PREWARM_BUFFER
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} PrewarmType;
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static char blockbuffer[BLCKSZ];
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/*
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* pg_prewarm(regclass, mode text, fork text,
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* first_block int8, last_block int8)
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*
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* The first argument is the relation to be prewarmed; the second controls
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* how prewarming is done; legal options are 'prefetch', 'read', and 'buffer'.
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* The third is the name of the relation fork to be prewarmed. The fourth
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* and fifth arguments specify the first and last block to be prewarmed.
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* If the fourth argument is NULL, it will be taken as 0; if the fifth argument
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* is NULL, it will be taken as the number of blocks in the relation. The
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* return value is the number of blocks successfully prewarmed.
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*/
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Datum
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pg_prewarm(PG_FUNCTION_ARGS)
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{
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Oid relOid;
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text *forkName;
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text *type;
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int64 first_block;
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int64 last_block;
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int64 nblocks;
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int64 blocks_done = 0;
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int64 block;
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Relation rel;
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ForkNumber forkNumber;
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char *forkString;
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char *ttype;
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PrewarmType ptype;
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AclResult aclresult;
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/* Basic sanity checking. */
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if (PG_ARGISNULL(0))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("relation cannot be null")));
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relOid = PG_GETARG_OID(0);
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if (PG_ARGISNULL(1))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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(errmsg("prewarm type cannot be null"))));
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type = PG_GETARG_TEXT_P(1);
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ttype = text_to_cstring(type);
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if (strcmp(ttype, "prefetch") == 0)
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ptype = PREWARM_PREFETCH;
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else if (strcmp(ttype, "read") == 0)
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ptype = PREWARM_READ;
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else if (strcmp(ttype, "buffer") == 0)
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ptype = PREWARM_BUFFER;
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else
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{
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("invalid prewarm type"),
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errhint("Valid prewarm types are \"prefetch\", \"read\", and \"buffer\".")));
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PG_RETURN_INT64(0); /* Placate compiler. */
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}
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if (PG_ARGISNULL(2))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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(errmsg("relation fork cannot be null"))));
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forkName = PG_GETARG_TEXT_P(2);
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forkString = text_to_cstring(forkName);
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forkNumber = forkname_to_number(forkString);
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/* Open relation and check privileges. */
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rel = relation_open(relOid, AccessShareLock);
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aclresult = pg_class_aclcheck(relOid, GetUserId(), ACL_SELECT);
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if (aclresult != ACLCHECK_OK)
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aclcheck_error(aclresult, ACL_KIND_CLASS, get_rel_name(relOid));
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/* Check that the fork exists. */
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RelationOpenSmgr(rel);
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if (!smgrexists(rel->rd_smgr, forkNumber))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("fork \"%s\" does not exist for this relation",
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forkString)));
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/* Validate block numbers, or handle nulls. */
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nblocks = RelationGetNumberOfBlocksInFork(rel, forkNumber);
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if (PG_ARGISNULL(3))
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first_block = 0;
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else
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{
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first_block = PG_GETARG_INT64(3);
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if (first_block < 0 || first_block >= nblocks)
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("starting block number must be between 0 and " INT64_FORMAT,
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nblocks - 1)));
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}
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if (PG_ARGISNULL(4))
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last_block = nblocks - 1;
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else
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{
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last_block = PG_GETARG_INT64(4);
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if (last_block < 0 || last_block >= nblocks)
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("ending block number must be between 0 and " INT64_FORMAT,
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nblocks - 1)));
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}
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/* Now we're ready to do the real work. */
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if (ptype == PREWARM_PREFETCH)
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{
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#ifdef USE_PREFETCH
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/*
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* In prefetch mode, we just hint the OS to read the blocks, but we
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* don't know whether it really does it, and we don't wait for it to
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* finish.
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*
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* It would probably be better to pass our prefetch requests in chunks
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* of a megabyte or maybe even a whole segment at a time, but there's
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* no practical way to do that at present without a gross modularity
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* violation, so we just do this.
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*/
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for (block = first_block; block <= last_block; ++block)
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{
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PrefetchBuffer(rel, forkNumber, block);
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++blocks_done;
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}
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#else
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("prefetch is not supported by this build")));
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#endif
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}
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else if (ptype == PREWARM_READ)
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{
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/*
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* In read mode, we actually read the blocks, but not into shared
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* buffers. This is more portable than prefetch mode (it works
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* everywhere) and is synchronous.
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*/
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for (block = first_block; block <= last_block; ++block)
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{
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smgrread(rel->rd_smgr, forkNumber, block, blockbuffer);
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++blocks_done;
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}
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}
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else if (ptype == PREWARM_BUFFER)
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{
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/*
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* In buffer mode, we actually pull the data into shared_buffers.
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*/
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for (block = first_block; block <= last_block; ++block)
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{
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Buffer buf;
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buf = ReadBufferExtended(rel, forkNumber, block, RBM_NORMAL, NULL);
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ReleaseBuffer(buf);
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++blocks_done;
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}
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}
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/* Close relation, release lock. */
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relation_close(rel, AccessShareLock);
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PG_RETURN_INT64(blocks_done);
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}

‎contrib/pg_prewarm/pg_prewarm.control

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# pg_prewarm extension
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comment = 'prewarm relation data'
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default_version = '1.0'
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module_pathname = '$libdir/pg_prewarm'
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relocatable = true

‎doc/src/sgml/contrib.sgml

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@@ -128,6 +128,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
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&pgbuffercache;
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&pgcrypto;
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&pgfreespacemap;
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&pgprewarm;
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&pgrowlocks;
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&pgstatstatements;
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&pgstattuple;

‎doc/src/sgml/filelist.sgml

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<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">
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<!ENTITY pgcrypto SYSTEM "pgcrypto.sgml">
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<!ENTITY pgfreespacemap SYSTEM "pgfreespacemap.sgml">
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<!ENTITY pgprewarm SYSTEM "pgprewarm.sgml">
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<!ENTITY pgrowlocks SYSTEM "pgrowlocks.sgml">
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<!ENTITY pgstandby SYSTEM "pgstandby.sgml">
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<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">

‎doc/src/sgml/pgprewarm.sgml

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<!-- doc/src/sgml/pgprewarm.sgml -->
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<sect1 id="pgprewarm" xreflabel="pg_prewarm">
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<title>pg_prewarm</title>
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<indexterm zone="pgprewarm">
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<primary>pg_prewarm</primary>
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</indexterm>
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<para>
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The <filename>pg_prewarm</filename> module provides a convenient way
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to load relation data into either the operating system buffer cache
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or the <productname>PostgreSQL</productname> buffer cache.
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</para>
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<sect2>
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<title>Functions</title>
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<synopsis>
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pg_prewarm(regclass, mode text default 'buffer', fork text default 'main',
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first_block int8 default null,
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last_block int8 default null) RETURNS int8
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</synopsis>
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<para>
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The first argument is the relation to be prewarmed. The second argument
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is the prewarming method to be used, as further discussed below; the third
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is the relation fork to be prewarmed, usually <literal>main</literal>.
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The fourth argument is the first block number to prewarm
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(<literal>NULL</literal> is accepted as a synonym for zero). The fifth
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argument is the last block number to prewarm (<literal>NULL</literal>
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means prewarm through the last block in the relation). The return value
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is the number of blocks prewarmed.
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</para>
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<para>
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There are three available prewarming methods. <literal>prefetch</literal>
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issues asynchronous prefetch requests to the operating system, if this is
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supported, or throws an error otherwise. <literal>read</literal> reads
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the requested range of blocks; unlike <literal>prefetch</literal>, this is
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synchronous and supported on all platforms and builds, but may be slower.
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<literal>buffer</literal> reads the requested range of blocks into the
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database buffer cache.
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</para>
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<para>
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Note that with any of these methods, attempting to prewarm more blocks than
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can be cached &mdash; by the OS when using <literal>prefetch</literal> or
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<literal>read</literal>, or by <productname>PostgreSQL</productname> when
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using <literal>buffer</literal> &mdash; will likely result in lower-numbered
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blocks being evicted as higher numbered blocks are read in. Prewarmed data
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also enjoys no special protection from cache evictions, so it is possible
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for other system activity may evict the newly prewarmed blocks shortly after
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they are read; conversely, prewarming may also evict other data from cache.
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For these reasons, prewarming is typically most useful at startup, when
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caches are largely empty.
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</para>
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</sect2>
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<sect2>
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<title>Author</title>
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<para>
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Robert Haas <email>rhaas@postgresql.org</email>
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</para>
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</sect2>
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</sect1>

‎src/tools/pgindent/typedefs.list

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PostgresPollingStatusType
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PostingItem
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PreParseColumnRefHook
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PrewarmType
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PredClass
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PredIterInfo
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PredIterInfoData

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