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/*-------------------------------------------------------------------------
*
* buf_init.c
* buffer manager initialization routines
*
* 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_init.c,v 1.72 2005/03/04 20:21:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "storage/bufmgr.h"
#include "storage/buf_internals.h"
BufferDesc *BufferDescriptors;
Block *BufferBlockPointers;
int32 *PrivateRefCount;
static char *BufferBlocks;
/* statistics counters */
long int ReadBufferCount;
long int ReadLocalBufferCount;
long int BufferHitCount;
long int LocalBufferHitCount;
long int BufferFlushCount;
long int LocalBufferFlushCount;
/*
* Data Structures:
* buffers live in a freelist and a lookup data structure.
*
*
* Buffer Lookup:
* Two important notes. First, the buffer has to be
* available for lookup BEFORE an IO begins. Otherwise
* a second process trying to read the buffer will
* allocate its own copy and the buffer pool will
* become inconsistent.
*
* Buffer Replacement:
* see freelist.c. A buffer cannot be replaced while in
* use either by data manager or during IO.
*
*
* Synchronization/Locking:
*
* IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
* It must be set when an IO is initiated and cleared at
* the end of the IO. It is there to make sure that one
* process doesn't start to use a buffer while another is
* faulting it in. see WaitIO and related routines.
*
* refcount -- Counts the number of processes holding pins on a buffer.
* A buffer is pinned during IO and immediately after a BufferAlloc().
* Pins must be released before end of transaction.
*
* PrivateRefCount -- Each buffer also has a private refcount that keeps
* track of the number of times the buffer is pinned in the current
* process. This is used for two purposes: first, if we pin a
* a buffer more than once, we only need to change the shared refcount
* once, thus only lock the shared state once; second, when a transaction
* aborts, it should only unpin the buffers exactly the number of times it
* has pinned them, so that it will not blow away buffers of another
* backend.
*/
/*
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
* postmaster, or in a standalone backend).
*/
void
InitBufferPool(void)
{
bool foundBufs,
foundDescs;
BufferDescriptors = (BufferDesc *)
ShmemInitStruct("Buffer Descriptors",
NBuffers * sizeof(BufferDesc), &foundDescs);
BufferBlocks = (char *)
ShmemInitStruct("Buffer Blocks",
NBuffers * BLCKSZ, &foundBufs);
if (foundDescs || foundBufs)
{
/* both should be present or neither */
Assert(foundDescs && foundBufs);
/* note: this path is only taken in EXEC_BACKEND case */
}
else
{
BufferDesc *buf;
int i;
buf = BufferDescriptors;
/*
* Initialize all the buffer headers.
*/
for (i = 0; i < NBuffers; buf++, i++)
{
CLEAR_BUFFERTAG(buf->tag);
buf->flags = 0;
buf->usage_count = 0;
buf->refcount = 0;
buf->wait_backend_id = 0;
SpinLockInit(&buf->buf_hdr_lock);
buf->buf_id = i;
/*
* Initially link all the buffers together as unused.
* Subsequent management of this list is done by freelist.c.
*/
buf->freeNext = i + 1;
buf->io_in_progress_lock = LWLockAssign();
buf->content_lock = LWLockAssign();
}
/* Correct last entry of linked list */
BufferDescriptors[NBuffers - 1].freeNext = FREENEXT_END_OF_LIST;
}
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
}
/*
* Initialize access to shared buffer pool
*
* This is called during backend startup (whether standalone or under the
* postmaster). It sets up for this backend's access to the already-existing
* buffer pool.
*
* NB: this is called before InitProcess(), so we do not have a PGPROC and
* cannot do LWLockAcquire; hence we can't actually access stuff in
* shared memory yet. We are only initializing local data here.
*/
void
InitBufferPoolAccess(void)
{
char *block;
int i;
/*
* Allocate and zero local arrays of per-buffer info.
*/
BufferBlockPointers = (Block *) calloc(NBuffers,
sizeof(*BufferBlockPointers));
PrivateRefCount = (int32 *) calloc(NBuffers,
sizeof(*PrivateRefCount));
/*
* Construct addresses for the individual buffer data blocks. We do
* this just to speed up the BufferGetBlock() macro. (Since the
* addresses should be the same in every backend, we could inherit
* this data from the postmaster --- but in the EXEC_BACKEND case
* that doesn't work.)
*/
block = BufferBlocks;
for (i = 0; i < NBuffers; i++)
{
BufferBlockPointers[i] = (Block) block;
block += BLCKSZ;
}
}
/*
* BufferShmemSize
*
* compute the size of shared memory for the buffer pool including
* data pages, buffer descriptors, hash tables, etc.
*/
int
BufferShmemSize(void)
{
int size = 0;
/* size of buffer descriptors */
size += MAXALIGN(NBuffers * sizeof(BufferDesc));
/* size of data pages */
size += NBuffers * MAXALIGN(BLCKSZ);
/* size of stuff controlled by freelist.c */
size += StrategyShmemSize();
return size;
}
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