/*------------------------------------------------------------------------- * * buf_table.c * routines for mapping BufferTags to buffer indexes. * * Note: the routines in this file do no locking of their own. The caller * must hold a suitable lock on the BufMappingLock, as specified in the * comments. * * * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.40 2005/03/04 20:21:06 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "storage/buf_internals.h" #include "storage/bufmgr.h" /* entry for buffer lookup hashtable */ typedef struct { BufferTag key; /* Tag of a disk page */ int id; /* Associated buffer ID */ } BufferLookupEnt; static HTAB *SharedBufHash; /* * Estimate space needed for mapping hashtable * size is the desired hash table size (possibly more than NBuffers) */ int BufTableShmemSize(int size) { return hash_estimate_size(size, sizeof(BufferLookupEnt)); } /* * Initialize shmem hash table for mapping buffers * size is the desired hash table size (possibly more than NBuffers) */ void InitBufTable(int size) { HASHCTL info; /* assume no locking is needed yet */ /* BufferTag maps to Buffer */ info.keysize = sizeof(BufferTag); info.entrysize = sizeof(BufferLookupEnt); info.hash = tag_hash; SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table", size, size, &info, HASH_ELEM | HASH_FUNCTION); if (!SharedBufHash) elog(FATAL, "could not initialize shared buffer hash table"); } /* * BufTableLookup * Lookup the given BufferTag; return buffer ID, or -1 if not found * * Caller must hold at least share lock on BufMappingLock */ int BufTableLookup(BufferTag *tagPtr) { BufferLookupEnt *result; result = (BufferLookupEnt *) hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL); if (!result) return -1; return result->id; } /* * BufTableInsert * Insert a hashtable entry for given tag and buffer ID, * unless an entry already exists for that tag * * Returns -1 on successful insertion. If a conflicting entry exists * already, returns the buffer ID in that entry. * * Caller must hold write lock on BufMappingLock */ int BufTableInsert(BufferTag *tagPtr, int buf_id) { BufferLookupEnt *result; bool found; Assert(buf_id >= 0); /* -1 is reserved for not-in-table */ Assert(tagPtr->blockNum != P_NEW); /* invalid tag */ result = (BufferLookupEnt *) hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found); if (!result) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); if (found) /* found something already in the table */ return result->id; result->id = buf_id; return -1; } /* * BufTableDelete * Delete the hashtable entry for given tag (which must exist) * * Caller must hold write lock on BufMappingLock */ void BufTableDelete(BufferTag *tagPtr) { BufferLookupEnt *result; result = (BufferLookupEnt *) hash_search(SharedBufHash, (void *) tagPtr, HASH_REMOVE, NULL); if (!result) /* shouldn't happen */ elog(ERROR, "shared buffer hash table corrupted"); }