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/*-------------------------------------------------------------------------
*
* buf_init.c
* buffer manager initialization routines
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/storage/buffer/buf_init.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
BufferDescPadded *BufferDescriptors;
char *BufferBlocks;
LWLockMinimallyPadded *BufferIOLWLockArray = NULL;
WritebackContext BackendWritebackContext;
CkptSortItem *CkptBufferIds;
/*
* 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. For efficiency the
* shared refcount isn't increased if an individual backend pins a buffer
* multiple times. Check the PrivateRefCount infrastructure in bufmgr.c.
*/
/*
* 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,
foundIOLocks,
foundBufCkpt;
/* Align descriptors to a cacheline boundary. */
BufferDescriptors = (BufferDescPadded *)
ShmemInitStruct("Buffer Descriptors",
NBuffers * sizeof(BufferDescPadded),
&foundDescs);
BufferBlocks = (char *)
ShmemInitStruct("Buffer Blocks",
NBuffers * (Size) BLCKSZ, &foundBufs);
/* Align lwlocks to cacheline boundary */
BufferIOLWLockArray = (LWLockMinimallyPadded *)
ShmemInitStruct("Buffer IO Locks",
NBuffers * (Size) sizeof(LWLockMinimallyPadded),
&foundIOLocks);
LWLockRegisterTranche(LWTRANCHE_BUFFER_IO_IN_PROGRESS, "buffer_io");
LWLockRegisterTranche(LWTRANCHE_BUFFER_CONTENT, "buffer_content");
/*
* The array used to sort to-be-checkpointed buffer ids is located in
* shared memory, to avoid having to allocate significant amounts of
* memory at runtime. As that'd be in the middle of a checkpoint, or when
* the checkpointer is restarted, memory allocation failures would be
* painful.
*/
CkptBufferIds = (CkptSortItem *)
ShmemInitStruct("Checkpoint BufferIds",
NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
if (foundDescs || foundBufs || foundIOLocks || foundBufCkpt)
{
/* should find all of these, or none of them */
Assert(foundDescs && foundBufs && foundIOLocks && foundBufCkpt);
/* note: this path is only taken in EXEC_BACKEND case */
}
else
{
int i;
/*
* Initialize all the buffer headers.
*/
for (i = 0; i < NBuffers; i++)
{
BufferDesc *buf = GetBufferDescriptor(i);
CLEAR_BUFFERTAG(buf->tag);
pg_atomic_init_u32(&buf->state, 0);
buf->wait_backend_pid = 0;
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;
LWLockInitialize(BufferDescriptorGetContentLock(buf),
LWTRANCHE_BUFFER_CONTENT);
LWLockInitialize(BufferDescriptorGetIOLock(buf),
LWTRANCHE_BUFFER_IO_IN_PROGRESS);
}
/* Correct last entry of linked list */
GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
}
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
/* Initialize per-backend file flush context */
WritebackContextInit(&BackendWritebackContext,
&backend_flush_after);
}
/*
* BufferShmemSize
*
* compute the size of shared memory for the buffer pool including
* data pages, buffer descriptors, hash tables, etc.
*/
Size
BufferShmemSize(void)
{
Size size = 0;
/* size of buffer descriptors */
size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
/* to allow aligning buffer descriptors */
size = add_size(size, PG_CACHE_LINE_SIZE);
/* size of data pages */
size = add_size(size, mul_size(NBuffers, BLCKSZ));
/* size of stuff controlled by freelist.c */
size = add_size(size, StrategyShmemSize());
/*
* It would be nice to include the I/O locks in the BufferDesc, but that
* would increase the size of a BufferDesc to more than one cache line,
* and benchmarking has shown that keeping every BufferDesc aligned on a
* cache line boundary is important for performance. So, instead, the
* array of I/O locks is allocated in a separate tranche. Because those
* locks are not highly contended, we lay out the array with minimal
* padding.
*/
size = add_size(size, mul_size(NBuffers, sizeof(LWLockMinimallyPadded)));
/* to allow aligning the above */
size = add_size(size, PG_CACHE_LINE_SIZE);
/* size of checkpoint sort array in bufmgr.c */
size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
return size;
}
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