mirror of https://github.com/postgres/postgres
Neil Conway
21 years ago
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# $PostgreSQL: pgsql/contrib/pg_buffercache/Makefile,v 1.1 2005/03/12 15:36:24 neilc Exp $
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MODULE_big = pg_buffercache
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OBJS = pg_buffercache_pages.o
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DATA_built = pg_buffercache.sql
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DOCS = README.pg_buffercache
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ifdef USE_PGXS |
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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_buffercache
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global |
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include $(top_srcdir)/contrib/contrib-global.mk |
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endif |
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Pg_buffercache - Real time queries on the shared buffer cache. |
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-------------- |
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This module consists of a C function 'pg_buffercache_pages()' that returns |
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a set of records, plus a view 'pg_buffercache' to wrapper the function. |
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The intent is to do for the buffercache what pg_locks does for locks, i.e - |
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ability to examine what is happening at any given time without having to |
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restart or rebuild the server with debugging code added. |
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By default public access is REVOKED from both of these, just in case there |
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are security issues lurking. |
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Installation |
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------------ |
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Build and install the main Postgresql source, then this contrib module: |
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$ cd contrib/pg_buffercache |
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$ gmake |
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$ gmake install |
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To register the functions: |
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$ psql -d <database> -f pg_buffercache.sql |
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Notes |
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----- |
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The definition of the columns exposed in the view is: |
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Column | references | Description |
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----------------+----------------------+------------------------------------ |
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bufferid | | Id, 1->shared_buffers. |
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relfilenode | pg_class.relfilenode | Refilenode of the relation. |
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reltablespace | pg_tablespace.oid | Tablespace oid of the relation. |
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reldatabase | pg_database.oid | Database for the relation. |
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relblocknumber | | Offset of the page in the relation. |
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isdirty | | Is the page dirty? |
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There is one row for each buffer in the shared cache. Unused buffers are |
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shown with all fields null except bufferid. |
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Because the cache is shared by all the databases, there are pages from |
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relations not belonging to the current database. |
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When the pg_buffercache view is accessed, internal buffer manager locks are |
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taken, and a copy of the buffer cache data is made for the view to display. |
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This ensures that the view produces a consistent set of results, while not |
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blocking normal buffer activity longer than necessary. Nonetheless there |
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could be some impact on database performance if this view is read often. |
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Sample output |
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------------- |
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regression=# \d pg_buffercache; |
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View "public.pg_buffercache" |
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Column | Type | Modifiers |
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----------------+---------+----------- |
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bufferid | integer | |
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relfilenode | oid | |
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reltablespace | oid | |
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reldatabase | oid | |
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relblocknumber | numeric | |
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isdirty | boolean | |
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View definition: |
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SELECT p.bufferid, p.relfilenode, p.reltablespace, p.reldatabase, |
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p.relblocknumber, p.isdirty |
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FROM pg_buffercache_pages() p(bufferid integer, relfilenode oid, |
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reltablespace oid, reldatabase oid, relblocknumber numeric(10,0), |
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isdirty boolean); |
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regression=# SELECT c.relname, count(*) AS buffers |
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FROM pg_class c, pg_buffercache b |
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WHERE b.relfilenode = c.relfilenode |
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GROUP BY c.relname |
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ORDER BY 2 DESC LIMIT 10; |
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relname | buffers |
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---------------------------------+--------- |
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tenk2 | 345 |
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tenk1 | 141 |
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pg_proc | 46 |
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pg_class | 45 |
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pg_attribute | 43 |
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pg_class_relname_nsp_index | 30 |
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pg_proc_proname_args_nsp_index | 28 |
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pg_attribute_relid_attnam_index | 26 |
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pg_depend | 22 |
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pg_depend_reference_index | 20 |
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(10 rows) |
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regression=# |
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Author |
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------ |
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* Mark Kirkwood <markir@paradise.net.nz> |
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Help |
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---- |
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* Design suggestions : Neil Conway <neilc@samurai.com> |
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* Debugging advice : Tom Lane <tgl@sss.pgh.pa.us> |
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Thanks guys! |
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@ -0,0 +1,18 @@ |
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-- Adjust this setting to control where the objects get created. |
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SET search_path = public; |
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-- Register the function. |
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CREATE OR REPLACE FUNCTION pg_buffercache_pages() |
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RETURNS SETOF RECORD |
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AS 'MODULE_PATHNAME', 'pg_buffercache_pages' |
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LANGUAGE 'C'; |
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-- Create a view for convenient access. |
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CREATE VIEW pg_buffercache AS |
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SELECT P.* FROM pg_buffercache_pages() AS P |
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(bufferid integer, relfilenode oid, reltablespace oid, reldatabase oid, |
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relblocknumber numeric(10), isdirty bool); |
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-- Don't want these to be available at public. |
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REVOKE ALL ON FUNCTION pg_buffercache_pages() FROM PUBLIC; |
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REVOKE ALL ON pg_buffercache FROM PUBLIC; |
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@ -0,0 +1,238 @@ |
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/*-------------------------------------------------------------------------
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* |
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* pg_buffercache_pages.c |
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* display some contents of the buffer cache |
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* |
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* $PostgreSQL: pgsql/contrib/pg_buffercache/pg_buffercache_pages.c,v 1.1 2005/03/12 15:36:24 neilc Exp $ |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "funcapi.h" |
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#include "catalog/pg_type.h" |
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#include "storage/buf_internals.h" |
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#include "storage/bufmgr.h" |
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#include "utils/relcache.h" |
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#include "pg_buffercache_pages.h" |
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#define NUM_BUFFERCACHE_PAGES_ELEM 6 |
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/*
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* Record structure holding the to be exposed cache data. |
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*/ |
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typedef struct |
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{ |
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uint32 bufferid; |
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Oid relfilenode; |
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Oid reltablespace; |
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Oid reldatabase; |
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BlockNumber blocknum; |
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bool isvalid; |
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bool isdirty; |
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} BufferCachePagesRec; |
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/*
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* Function context for data persisting over repeated calls. |
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*/ |
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typedef struct
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{ |
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AttInMetadata *attinmeta; |
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BufferCachePagesRec *record; |
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char *values[NUM_BUFFERCACHE_PAGES_ELEM]; |
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} BufferCachePagesContext; |
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/*
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* Function returning data from the shared buffer cache - buffer number, |
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* relation node/tablespace/database/blocknum and dirty indicator. |
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*/ |
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PG_FUNCTION_INFO_V1(pg_buffercache_pages); |
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Datum |
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pg_buffercache_pages(PG_FUNCTION_ARGS) |
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{ |
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FuncCallContext *funcctx; |
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Datum result; |
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MemoryContext oldcontext; |
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BufferCachePagesContext *fctx; /* User function context. */ |
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TupleDesc tupledesc; |
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HeapTuple tuple; |
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if (SRF_IS_FIRSTCALL()) |
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{ |
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RelFileNode rnode; |
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uint32 i; |
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BufferDesc *bufHdr; |
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funcctx = SRF_FIRSTCALL_INIT(); |
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/* Switch context when allocating stuff to be used in later calls */ |
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oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx); |
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/* Construct a tuple to return. */ |
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tupledesc = CreateTemplateTupleDesc(NUM_BUFFERCACHE_PAGES_ELEM, false); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 1, "bufferid", |
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INT4OID, -1, 0); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 2, "relfilenode", |
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OIDOID, -1, 0); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 3, "reltablespace", |
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OIDOID, -1, 0); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 4, "reldatabase", |
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OIDOID, -1, 0); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 5, "relblockbumber", |
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NUMERICOID, -1, 0); |
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TupleDescInitEntry(tupledesc, (AttrNumber) 6, "isdirty", |
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BOOLOID, -1, 0); |
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/* Generate attribute metadata needed later to produce tuples */ |
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funcctx->attinmeta = TupleDescGetAttInMetadata(tupledesc); |
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/*
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* Create a function context for cross-call persistence
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* and initialize the buffer counters. |
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*/ |
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fctx = (BufferCachePagesContext *) palloc(sizeof(BufferCachePagesContext)); |
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funcctx->max_calls = NBuffers; |
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funcctx->user_fctx = fctx; |
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/* Allocate NBuffers worth of BufferCachePagesRec records. */ |
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fctx->record = (BufferCachePagesRec *) palloc(sizeof(BufferCachePagesRec) * NBuffers); |
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/* allocate the strings for tuple formation */ |
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fctx->values[0] = (char *) palloc(3 * sizeof(uint32) + 1); |
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fctx->values[1] = (char *) palloc(3 * sizeof(uint32) + 1); |
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fctx->values[2] = (char *) palloc(3 * sizeof(uint32) + 1); |
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fctx->values[3] = (char *) palloc(3 * sizeof(uint32) + 1); |
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fctx->values[4] = (char *) palloc(3 * sizeof(uint32) + 1); |
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fctx->values[5] = (char *) palloc(2); |
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/* Return to original context when allocating transient memory */ |
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MemoryContextSwitchTo(oldcontext); |
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/*
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* Lock Buffer map and scan though all the buffers, saving the |
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* relevant fields in the fctx->record structure. |
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*/ |
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LWLockAcquire(BufMappingLock, LW_SHARED); |
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for (i = 0, bufHdr = BufferDescriptors; i < NBuffers; i++, bufHdr++) |
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{ |
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/* Lock each buffer header before inspecting. */ |
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LockBufHdr(bufHdr); |
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rnode = bufHdr->tag.rnode; |
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fctx->record[i].bufferid = BufferDescriptorGetBuffer(bufHdr); |
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fctx->record[i].relfilenode = rnode.relNode; |
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fctx->record[i].reltablespace = rnode.spcNode; |
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fctx->record[i].reldatabase = rnode.dbNode; |
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fctx->record[i].blocknum = bufHdr->tag.blockNum; |
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if ( bufHdr->flags & BM_DIRTY)
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{ |
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fctx->record[i].isdirty = true; |
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} |
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else |
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{ |
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fctx->record[i].isdirty = false; |
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} |
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/* Note if the buffer is valid, and has storage created */ |
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if ( (bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_TAG_VALID)) |
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{ |
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fctx->record[i].isvalid = true; |
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} |
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else |
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{ |
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fctx->record[i].isvalid = false; |
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} |
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UnlockBufHdr(bufHdr); |
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} |
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/* Release Buffer map. */ |
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LWLockRelease(BufMappingLock); |
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} |
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funcctx = SRF_PERCALL_SETUP(); |
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/* Get the saved state */ |
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fctx = funcctx->user_fctx; |
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if (funcctx->call_cntr < funcctx->max_calls) |
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{ |
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uint32 i = funcctx->call_cntr; |
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char *values[NUM_BUFFERCACHE_PAGES_ELEM]; |
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int j; |
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/*
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* Use a temporary values array, initially pointing to |
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* fctx->values, so it can be reassigned w/o losing the storage |
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* for subsequent calls. |
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*/ |
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for (j = 0; j < NUM_BUFFERCACHE_PAGES_ELEM; j++) |
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{ |
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values[j] = fctx->values[j]; |
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} |
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/*
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* Set all fields except the bufferid to null if the buffer is |
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* unused or not valid. |
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*/ |
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if (fctx->record[i].blocknum == InvalidBlockNumber || |
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fctx->record[i].isvalid == false ) |
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{ |
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sprintf(values[0], "%u", fctx->record[i].bufferid); |
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values[1] = NULL; |
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values[2] = NULL; |
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values[3] = NULL; |
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values[4] = NULL; |
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values[5] = NULL; |
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} |
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else |
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{ |
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sprintf(values[0], "%u", fctx->record[i].bufferid); |
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sprintf(values[1], "%u", fctx->record[i].relfilenode); |
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sprintf(values[2], "%u", fctx->record[i].reltablespace); |
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sprintf(values[3], "%u", fctx->record[i].reldatabase); |
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sprintf(values[4], "%u", fctx->record[i].blocknum); |
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if (fctx->record[i].isdirty)
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{ |
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strcpy(values[5], "t"); |
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} |
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else |
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{ |
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strcpy(values[5], "f"); |
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} |
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} |
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/* Build and return the tuple. */ |
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tuple = BuildTupleFromCStrings(funcctx->attinmeta, values); |
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result = HeapTupleGetDatum(tuple); |
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SRF_RETURN_NEXT(funcctx, result); |
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} |
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else |
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SRF_RETURN_DONE(funcctx); |
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} |
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@ -0,0 +1,18 @@ |
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/*-------------------------------------------------------------------------
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* |
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* pg_buffercache_pages.h |
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* Prototypes for pg_buffercache_pages |
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* |
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* |
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* $PostgreSQL: pgsql/contrib/pg_buffercache/pg_buffercache_pages.h,v 1.1 2005/03/12 15:36:24 neilc Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#ifndef PG_BUFFERCACHE_PAGES_H |
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#define PG_BUFFERCACHE_PAGES_H |
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extern Datum pg_buffercache_pages(PG_FUNCTION_ARGS); |
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#endif /* PG_BUFFERCACHE_PAGES_H */ |
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