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/*-------------------------------------------------------------------------
*
* buf_internals.h
* Internal definitions for buffer manager and the buffer replacement
* strategy.
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.96 2008/06/12 09:12:31 heikki Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef BUFMGR_INTERNALS_H
#define BUFMGR_INTERNALS_H
#include "storage/buf.h"
#include "storage/lwlock.h"
#include "storage/shmem.h"
#include "storage/smgr.h"
#include "storage/spin.h"
#include "utils/rel.h"
/*
* Flags for buffer descriptors
*
* Note: TAG_VALID essentially means that there is a buffer hashtable
* entry associated with the buffer's tag.
*/
#define BM_DIRTY (1 << 0) /* data needs writing */
#define BM_VALID (1 << 1) /* data is valid */
#define BM_TAG_VALID (1 << 2) /* tag is assigned */
#define BM_IO_IN_PROGRESS (1 << 3) /* read or write in progress */
#define BM_IO_ERROR (1 << 4) /* previous I/O failed */
#define BM_JUST_DIRTIED (1 << 5) /* dirtied since write started */
#define BM_PIN_COUNT_WAITER (1 << 6) /* have waiter for sole pin */
#define BM_CHECKPOINT_NEEDED (1 << 7) /* must write for checkpoint */
typedef bits16 BufFlags;
/*
* The maximum allowed value of usage_count represents a tradeoff between
* accuracy and speed of the clock-sweep buffer management algorithm. A
* large value (comparable to NBuffers) would approximate LRU semantics.
* But it can take as many as BM_MAX_USAGE_COUNT+1 complete cycles of
* clock sweeps to find a free buffer, so in practice we don't want the
* value to be very large.
*/
#define BM_MAX_USAGE_COUNT 5
/*
* Buffer tag identifies which disk block the buffer contains.
*
* Note: the BufferTag data must be sufficient to determine where to write the
* block, without reference to pg_class or pg_tablespace entries. It's
* possible that the backend flushing the buffer doesn't even believe the
* relation is visible yet (its xact may have started before the xact that
* created the rel). The storage manager must be able to cope anyway.
*
* Note: if there's any pad bytes in the struct, INIT_BUFFERTAG will have
* to be fixed to zero them, since this struct is used as a hash key.
*/
typedef struct buftag
{
RelFileNode rnode; /* physical relation identifier */
BlockNumber blockNum; /* blknum relative to begin of reln */
} BufferTag;
#define CLEAR_BUFFERTAG(a) \
( \
(a).rnode.spcNode = InvalidOid, \
(a).rnode.dbNode = InvalidOid, \
(a).rnode.relNode = InvalidOid, \
(a).blockNum = InvalidBlockNumber \
)
#define INIT_BUFFERTAG(a,xx_rnode,xx_blockNum) \
( \
(a).rnode = (xx_rnode), \
(a).blockNum = (xx_blockNum) \
)
#define BUFFERTAGS_EQUAL(a,b) \
( \
RelFileNodeEquals((a).rnode, (b).rnode) && \
(a).blockNum == (b).blockNum \
)
/*
* The shared buffer mapping table is partitioned to reduce contention.
* To determine which partition lock a given tag requires, compute the tag's
* hash code with BufTableHashCode(), then apply BufMappingPartitionLock().
* NB: NUM_BUFFER_PARTITIONS must be a power of 2!
*/
#define BufTableHashPartition(hashcode) \
((hashcode) % NUM_BUFFER_PARTITIONS)
#define BufMappingPartitionLock(hashcode) \
((LWLockId) (FirstBufMappingLock + BufTableHashPartition(hashcode)))
/*
* BufferDesc -- shared descriptor/state data for a single shared buffer.
*
* Note: buf_hdr_lock must be held to examine or change the tag, flags,
* usage_count, refcount, or wait_backend_pid fields. buf_id field never
* changes after initialization, so does not need locking. freeNext is
* protected by the BufFreelistLock not buf_hdr_lock. The LWLocks can take
* care of themselves. The buf_hdr_lock is *not* used to control access to
* the data in the buffer!
*
* An exception is that if we have the buffer pinned, its tag can't change
* underneath us, so we can examine the tag without locking the spinlock.
* Also, in places we do one-time reads of the flags without bothering to
* lock the spinlock; this is generally for situations where we don't expect
* the flag bit being tested to be changing.
*
* We can't physically remove items from a disk page if another backend has
* the buffer pinned. Hence, a backend may need to wait for all other pins
* to go away. This is signaled by storing its own PID into
* wait_backend_pid and setting flag bit BM_PIN_COUNT_WAITER. At present,
* there can be only one such waiter per buffer.
*
* We use this same struct for local buffer headers, but the lock fields
* are not used and not all of the flag bits are useful either.
*/
typedef struct sbufdesc
{
BufferTag tag; /* ID of page contained in buffer */
BufFlags flags; /* see bit definitions above */
uint16 usage_count; /* usage counter for clock sweep code */
unsigned refcount; /* # of backends holding pins on buffer */
int wait_backend_pid; /* backend PID of pin-count waiter */
slock_t buf_hdr_lock; /* protects the above fields */
int buf_id; /* buffer's index number (from 0) */
int freeNext; /* link in freelist chain */
LWLockId io_in_progress_lock; /* to wait for I/O to complete */
LWLockId content_lock; /* to lock access to buffer contents */
} BufferDesc;
#define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)
/*
* The freeNext field is either the index of the next freelist entry,
* or one of these special values:
*/
#define FREENEXT_END_OF_LIST (-1)
#define FREENEXT_NOT_IN_LIST (-2)
/*
* Macros for acquiring/releasing a shared buffer header's spinlock.
* Do not apply these to local buffers!
*
* Note: as a general coding rule, if you are using these then you probably
* need to be using a volatile-qualified pointer to the buffer header, to
* ensure that the compiler doesn't rearrange accesses to the header to
* occur before or after the spinlock is acquired/released.
*/
#define LockBufHdr(bufHdr) SpinLockAcquire(&(bufHdr)->buf_hdr_lock)
#define UnlockBufHdr(bufHdr) SpinLockRelease(&(bufHdr)->buf_hdr_lock)
/* in buf_init.c */
extern PGDLLIMPORT BufferDesc *BufferDescriptors;
/* in localbuf.c */
extern BufferDesc *LocalBufferDescriptors;
/* event counters in buf_init.c */
extern long int ReadBufferCount;
extern long int ReadLocalBufferCount;
extern long int BufferHitCount;
extern long int LocalBufferHitCount;
extern long int BufferFlushCount;
extern long int LocalBufferFlushCount;
/*
* Internal routines: only called by bufmgr
*/
/* freelist.c */
extern volatile BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy,
bool *lock_held);
extern void StrategyFreeBuffer(volatile BufferDesc *buf);
extern bool StrategyRejectBuffer(BufferAccessStrategy strategy,
volatile BufferDesc *buf);
extern int StrategySyncStart(uint32 *complete_passes, uint32 *num_buf_alloc);
extern Size StrategyShmemSize(void);
extern void StrategyInitialize(bool init);
/* buf_table.c */
extern Size BufTableShmemSize(int size);
extern void InitBufTable(int size);
extern uint32 BufTableHashCode(BufferTag *tagPtr);
extern int BufTableLookup(BufferTag *tagPtr, uint32 hashcode);
extern int BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id);
extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode);
/* localbuf.c */
extern BufferDesc *LocalBufferAlloc(SMgrRelation reln, BlockNumber blockNum,
bool *foundPtr);
extern void MarkLocalBufferDirty(Buffer buffer);
extern void DropRelFileNodeLocalBuffers(RelFileNode rnode,
BlockNumber firstDelBlock);
extern void AtEOXact_LocalBuffers(bool isCommit);
#endif /* BUFMGR_INTERNALS_H */
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