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/*-------------------------------------------------------------------------
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* Internal definitions for buffer manager and the buffer replacement
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* Portions Copyright (c) 1996-2009, 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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#ifndef BUFMGR_INTERNALS_H
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#define BUFMGR_INTERNALS_H
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#include "storage/buf.h"
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#include "storage/lwlock.h"
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#include "storage/shmem.h"
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#include "storage/smgr.h"
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#include "storage/spin.h"
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#include "utils/relcache.h"
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* Flags for buffer descriptors
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* Note: TAG_VALID essentially means that there is a buffer hashtable
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* entry associated with the buffer's tag.
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#define BM_DIRTY (1 << 0) /* data needs writing */
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#define BM_VALID (1 << 1) /* data is valid */
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#define BM_TAG_VALID (1 << 2) /* tag is assigned */
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#define BM_IO_IN_PROGRESS (1 << 3) /* read or write in progress */
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#define BM_IO_ERROR (1 << 4) /* previous I/O failed */
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#define BM_JUST_DIRTIED (1 << 5) /* dirtied since write started */
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#define BM_PIN_COUNT_WAITER (1 << 6) /* have waiter for sole pin */
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#define BM_CHECKPOINT_NEEDED (1 << 7) /* must write for checkpoint */
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typedef bits16 BufFlags;
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* The maximum allowed value of usage_count represents a tradeoff between
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* accuracy and speed of the clock-sweep buffer management algorithm. A
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* large value (comparable to NBuffers) would approximate LRU semantics.
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* But it can take as many as BM_MAX_USAGE_COUNT+1 complete cycles of
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* clock sweeps to find a free buffer, so in practice we don't want the
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* value to be very large.
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#define BM_MAX_USAGE_COUNT 5
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* Buffer tag identifies which disk block the buffer contains.
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* Note: the BufferTag data must be sufficient to determine where to write the
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* block, without reference to pg_class or pg_tablespace entries. It's
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* possible that the backend flushing the buffer doesn't even believe the
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* relation is visible yet (its xact may have started before the xact that
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* created the rel). The storage manager must be able to cope anyway.
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* Note: if there's any pad bytes in the struct, INIT_BUFFERTAG will have
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* to be fixed to zero them, since this struct is used as a hash key.
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RelFileNode rnode; /* physical relation identifier */
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BlockNumber blockNum; /* blknum relative to begin of reln */
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#define CLEAR_BUFFERTAG(a) \
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(a).rnode.spcNode = InvalidOid, \
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(a).rnode.dbNode = InvalidOid, \
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(a).rnode.relNode = InvalidOid, \
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(a).forkNum = InvalidForkNumber, \
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(a).blockNum = InvalidBlockNumber \
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#define INIT_BUFFERTAG(a,xx_rnode,xx_forkNum,xx_blockNum) \
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(a).rnode = (xx_rnode), \
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(a).forkNum = (xx_forkNum), \
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(a).blockNum = (xx_blockNum) \
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#define BUFFERTAGS_EQUAL(a,b) \
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RelFileNodeEquals((a).rnode, (b).rnode) && \
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(a).blockNum == (b).blockNum && \
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(a).forkNum == (b).forkNum \
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* The shared buffer mapping table is partitioned to reduce contention.
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* To determine which partition lock a given tag requires, compute the tag's
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* hash code with BufTableHashCode(), then apply BufMappingPartitionLock().
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* NB: NUM_BUFFER_PARTITIONS must be a power of 2!
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#define BufTableHashPartition(hashcode) \
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((hashcode) % NUM_BUFFER_PARTITIONS)
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#define BufMappingPartitionLock(hashcode) \
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((LWLockId) (FirstBufMappingLock + BufTableHashPartition(hashcode)))
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* BufferDesc -- shared descriptor/state data for a single shared buffer.
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* Note: buf_hdr_lock must be held to examine or change the tag, flags,
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* usage_count, refcount, or wait_backend_pid fields. buf_id field never
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* changes after initialization, so does not need locking. freeNext is
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* protected by the BufFreelistLock not buf_hdr_lock. The LWLocks can take
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* care of themselves. The buf_hdr_lock is *not* used to control access to
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* the data in the buffer!
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* An exception is that if we have the buffer pinned, its tag can't change
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* underneath us, so we can examine the tag without locking the spinlock.
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* Also, in places we do one-time reads of the flags without bothering to
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* lock the spinlock; this is generally for situations where we don't expect
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* the flag bit being tested to be changing.
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* We can't physically remove items from a disk page if another backend has
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* the buffer pinned. Hence, a backend may need to wait for all other pins
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* to go away. This is signaled by storing its own PID into
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* wait_backend_pid and setting flag bit BM_PIN_COUNT_WAITER. At present,
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* there can be only one such waiter per buffer.
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* We use this same struct for local buffer headers, but the lock fields
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* are not used and not all of the flag bits are useful either.
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typedef struct sbufdesc
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BufferTag tag; /* ID of page contained in buffer */
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BufFlags flags; /* see bit definitions above */
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uint16 usage_count; /* usage counter for clock sweep code */
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unsigned refcount; /* # of backends holding pins on buffer */
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int wait_backend_pid; /* backend PID of pin-count waiter */
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slock_t buf_hdr_lock; /* protects the above fields */
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int buf_id; /* buffer's index number (from 0) */
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int freeNext; /* link in freelist chain */
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LWLockId io_in_progress_lock; /* to wait for I/O to complete */
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LWLockId content_lock; /* to lock access to buffer contents */
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#define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)
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* The freeNext field is either the index of the next freelist entry,
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* or one of these special values:
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#define FREENEXT_END_OF_LIST (-1)
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#define FREENEXT_NOT_IN_LIST (-2)
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* Macros for acquiring/releasing a shared buffer header's spinlock.
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* Do not apply these to local buffers!
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* Note: as a general coding rule, if you are using these then you probably
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* need to be using a volatile-qualified pointer to the buffer header, to
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* ensure that the compiler doesn't rearrange accesses to the header to
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* occur before or after the spinlock is acquired/released.
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#define LockBufHdr(bufHdr) SpinLockAcquire(&(bufHdr)->buf_hdr_lock)
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#define UnlockBufHdr(bufHdr) SpinLockRelease(&(bufHdr)->buf_hdr_lock)
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extern PGDLLIMPORT BufferDesc *BufferDescriptors;
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extern BufferDesc *LocalBufferDescriptors;
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/* event counters in buf_init.c */
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extern long int ReadBufferCount;
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extern long int ReadLocalBufferCount;
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extern long int BufferHitCount;
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extern long int LocalBufferHitCount;
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extern long int BufferFlushCount;
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extern long int LocalBufferFlushCount;
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extern long int BufFileReadCount;
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extern long int BufFileWriteCount;
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* Internal routines: only called by bufmgr
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extern volatile BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy,
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extern void StrategyFreeBuffer(volatile BufferDesc *buf);
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extern bool StrategyRejectBuffer(BufferAccessStrategy strategy,
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volatile BufferDesc *buf);
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extern int StrategySyncStart(uint32 *complete_passes, uint32 *num_buf_alloc);
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extern Size StrategyShmemSize(void);
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extern void StrategyInitialize(bool init);
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extern Size BufTableShmemSize(int size);
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extern void InitBufTable(int size);
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extern uint32 BufTableHashCode(BufferTag *tagPtr);
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extern int BufTableLookup(BufferTag *tagPtr, uint32 hashcode);
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extern int BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id);
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extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode);
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extern void LocalPrefetchBuffer(SMgrRelation smgr, ForkNumber forkNum,
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BlockNumber blockNum);
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extern BufferDesc *LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum,
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BlockNumber blockNum, bool *foundPtr);
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extern void MarkLocalBufferDirty(Buffer buffer);
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extern void DropRelFileNodeLocalBuffers(RelFileNode rnode, ForkNumber forkNum,
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BlockNumber firstDelBlock);
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extern void AtEOXact_LocalBuffers(bool isCommit);
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#endif /* BUFMGR_INTERNALS_H */