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