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138 lines
3.2 KiB
C
138 lines
3.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* buf_table.c
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* routines for mapping BufferTags to buffer indexes.
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*
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* Note: the routines in this file do no locking of their own. The caller
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* must hold a suitable lock on the BufMappingLock, as specified in the
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* comments.
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*
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*
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* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.44 2006/03/05 15:58:36 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "storage/buf_internals.h"
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#include "storage/bufmgr.h"
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/* entry for buffer lookup hashtable */
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typedef struct
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{
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BufferTag key; /* Tag of a disk page */
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int id; /* Associated buffer ID */
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} BufferLookupEnt;
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static HTAB *SharedBufHash;
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/*
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* Estimate space needed for mapping hashtable
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* size is the desired hash table size (possibly more than NBuffers)
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*/
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Size
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BufTableShmemSize(int size)
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{
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return hash_estimate_size(size, sizeof(BufferLookupEnt));
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}
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/*
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* Initialize shmem hash table for mapping buffers
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* size is the desired hash table size (possibly more than NBuffers)
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*/
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void
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InitBufTable(int size)
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{
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HASHCTL info;
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/* assume no locking is needed yet */
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/* BufferTag maps to Buffer */
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info.keysize = sizeof(BufferTag);
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info.entrysize = sizeof(BufferLookupEnt);
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info.hash = tag_hash;
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SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
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size, size,
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&info,
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HASH_ELEM | HASH_FUNCTION);
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if (!SharedBufHash)
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elog(FATAL, "could not initialize shared buffer hash table");
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}
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/*
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* BufTableLookup
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* Lookup the given BufferTag; return buffer ID, or -1 if not found
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*
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* Caller must hold at least share lock on BufMappingLock
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*/
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int
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BufTableLookup(BufferTag *tagPtr)
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{
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BufferLookupEnt *result;
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result = (BufferLookupEnt *)
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hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL);
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if (!result)
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return -1;
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return result->id;
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}
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/*
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* BufTableInsert
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* Insert a hashtable entry for given tag and buffer ID,
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* unless an entry already exists for that tag
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*
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* Returns -1 on successful insertion. If a conflicting entry exists
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* already, returns the buffer ID in that entry.
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*
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* Caller must hold write lock on BufMappingLock
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*/
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int
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BufTableInsert(BufferTag *tagPtr, int buf_id)
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{
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BufferLookupEnt *result;
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bool found;
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Assert(buf_id >= 0); /* -1 is reserved for not-in-table */
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Assert(tagPtr->blockNum != P_NEW); /* invalid tag */
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result = (BufferLookupEnt *)
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hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found);
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if (found) /* found something already in the table */
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return result->id;
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result->id = buf_id;
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return -1;
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}
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/*
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* BufTableDelete
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* Delete the hashtable entry for given tag (which must exist)
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*
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* Caller must hold write lock on BufMappingLock
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*/
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void
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BufTableDelete(BufferTag *tagPtr)
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{
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BufferLookupEnt *result;
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result = (BufferLookupEnt *)
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hash_search(SharedBufHash, (void *) tagPtr, HASH_REMOVE, NULL);
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if (!result) /* shouldn't happen */
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elog(ERROR, "shared buffer hash table corrupted");
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}
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