src/include/storage/buf_internals.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * buf_internals.h
   4  *        Internal definitions for buffer manager and the buffer replacement
   5  *        strategy.
   6  *
   7  *
   8  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
   9  * Portions Copyright (c) 1994, Regents of the University of California
  10  *
  11  * $PostgreSQL$
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #ifndef BUFMGR_INTERNALS_H
  16 #define BUFMGR_INTERNALS_H
  17
  18 #include "storage/buf.h"
  19 #include "storage/lwlock.h"
  20 #include "storage/shmem.h"
  21 #include "storage/smgr.h"
  22 #include "storage/spin.h"
  23 #include "utils/relcache.h"
  24
  25
  26 /*
  27  * Flags for buffer descriptors
  28  *
  29  * Note: TAG_VALID essentially means that there is a buffer hashtable
  30  * entry associated with the buffer's tag.
  31  */
  32 #define BM_DIRTY                                (1 << 0)                /* data needs writing */
  33 #define BM_VALID                                (1 << 1)                /* data is valid */
  34 #define BM_TAG_VALID                    (1 << 2)                /* tag is assigned */
  35 #define BM_IO_IN_PROGRESS               (1 << 3)                /* read or write in progress */
  36 #define BM_IO_ERROR                             (1 << 4)                /* previous I/O failed */
  37 #define BM_JUST_DIRTIED                 (1 << 5)                /* dirtied since write started */
  38 #define BM_PIN_COUNT_WAITER             (1 << 6)                /* have waiter for sole pin */
  39 #define BM_CHECKPOINT_NEEDED    (1 << 7)                /* must write for checkpoint */
  40
  41 typedef bits16 BufFlags;
  42
  43 /*
  44  * The maximum allowed value of usage_count represents a tradeoff between
  45  * accuracy and speed of the clock-sweep buffer management algorithm.  A
  46  * large value (comparable to NBuffers) would approximate LRU semantics.
  47  * But it can take as many as BM_MAX_USAGE_COUNT+1 complete cycles of
  48  * clock sweeps to find a free buffer, so in practice we don't want the
  49  * value to be very large.
  50  */
  51 #define BM_MAX_USAGE_COUNT      5
  52
  53 /*
  54  * Buffer tag identifies which disk block the buffer contains.
  55  *
  56  * Note: the BufferTag data must be sufficient to determine where to write the
  57  * block, without reference to pg_class or pg_tablespace entries.  It's
  58  * possible that the backend flushing the buffer doesn't even believe the
  59  * relation is visible yet (its xact may have started before the xact that
  60  * created the rel).  The storage manager must be able to cope anyway.
  61  *
  62  * Note: if there's any pad bytes in the struct, INIT_BUFFERTAG will have
  63  * to be fixed to zero them, since this struct is used as a hash key.
  64  */
  65 typedef struct buftag
  66 {
  67         RelFileNode rnode;                      /* physical relation identifier */
  68         ForkNumber      forkNum;
  69         BlockNumber blockNum;           /* blknum relative to begin of reln */
  70 } BufferTag;
  71
  72 #define CLEAR_BUFFERTAG(a) \
  73 ( \
  74         (a).rnode.spcNode = InvalidOid, \
  75         (a).rnode.dbNode = InvalidOid, \
  76         (a).rnode.relNode = InvalidOid, \
  77         (a).forkNum = InvalidForkNumber, \
  78         (a).blockNum = InvalidBlockNumber \
  79 )
  80
  81 #define INIT_BUFFERTAG(a,xx_rnode,xx_forkNum,xx_blockNum) \
  82 ( \
  83         (a).rnode = (xx_rnode), \
  84         (a).forkNum = (xx_forkNum), \
  85         (a).blockNum = (xx_blockNum) \
  86 )
  87
  88 #define BUFFERTAGS_EQUAL(a,b) \
  89 ( \
  90         RelFileNodeEquals((a).rnode, (b).rnode) && \
  91         (a).blockNum == (b).blockNum && \
  92         (a).forkNum == (b).forkNum \
  93 )
  94
  95 /*
  96  * The shared buffer mapping table is partitioned to reduce contention.
  97  * To determine which partition lock a given tag requires, compute the tag's
  98  * hash code with BufTableHashCode(), then apply BufMappingPartitionLock().
  99  * NB: NUM_BUFFER_PARTITIONS must be a power of 2!
 100  */
 101 #define BufTableHashPartition(hashcode) \
 102         ((hashcode) % NUM_BUFFER_PARTITIONS)
 103 #define BufMappingPartitionLock(hashcode) \
 104         ((LWLockId) (FirstBufMappingLock + BufTableHashPartition(hashcode)))
 105
 106 /*
 107  *      BufferDesc -- shared descriptor/state data for a single shared buffer.
 108  *
 109  * Note: buf_hdr_lock must be held to examine or change the tag, flags,
 110  * usage_count, refcount, or wait_backend_pid fields.  buf_id field never
 111  * changes after initialization, so does not need locking.      freeNext is
 112  * protected by the BufFreelistLock not buf_hdr_lock.  The LWLocks can take
 113  * care of themselves.  The buf_hdr_lock is *not* used to control access to
 114  * the data in the buffer!
 115  *
 116  * An exception is that if we have the buffer pinned, its tag can't change
 117  * underneath us, so we can examine the tag without locking the spinlock.
 118  * Also, in places we do one-time reads of the flags without bothering to
 119  * lock the spinlock; this is generally for situations where we don't expect
 120  * the flag bit being tested to be changing.
 121  *
 122  * We can't physically remove items from a disk page if another backend has
 123  * the buffer pinned.  Hence, a backend may need to wait for all other pins
 124  * to go away.  This is signaled by storing its own PID into
 125  * wait_backend_pid and setting flag bit BM_PIN_COUNT_WAITER.  At present,
 126  * there can be only one such waiter per buffer.
 127  *
 128  * We use this same struct for local buffer headers, but the lock fields
 129  * are not used and not all of the flag bits are useful either.
 130  */
 131 typedef struct sbufdesc
 132 {
 133         BufferTag       tag;                    /* ID of page contained in buffer */
 134         BufFlags        flags;                  /* see bit definitions above */
 135         uint16          usage_count;    /* usage counter for clock sweep code */
 136         unsigned        refcount;               /* # of backends holding pins on buffer */
 137         int                     wait_backend_pid;               /* backend PID of pin-count waiter */
 138
 139         slock_t         buf_hdr_lock;   /* protects the above fields */
 140
 141         int                     buf_id;                 /* buffer's index number (from 0) */
 142         int                     freeNext;               /* link in freelist chain */
 143
 144         LWLockId        io_in_progress_lock;    /* to wait for I/O to complete */
 145         LWLockId        content_lock;   /* to lock access to buffer contents */
 146 } BufferDesc;
 147
 148 #define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)
 149
 150 /*
 151  * The freeNext field is either the index of the next freelist entry,
 152  * or one of these special values:
 153  */
 154 #define FREENEXT_END_OF_LIST    (-1)
 155 #define FREENEXT_NOT_IN_LIST    (-2)
 156
 157 /*
 158  * Macros for acquiring/releasing a shared buffer header's spinlock.
 159  * Do not apply these to local buffers!
 160  *
 161  * Note: as a general coding rule, if you are using these then you probably
 162  * need to be using a volatile-qualified pointer to the buffer header, to
 163  * ensure that the compiler doesn't rearrange accesses to the header to
 164  * occur before or after the spinlock is acquired/released.
 165  */
 166 #define LockBufHdr(bufHdr)              SpinLockAcquire(&(bufHdr)->buf_hdr_lock)
 167 #define UnlockBufHdr(bufHdr)    SpinLockRelease(&(bufHdr)->buf_hdr_lock)
 168
 169
 170 /* in buf_init.c */
 171 extern PGDLLIMPORT BufferDesc *BufferDescriptors;
 172
 173 /* in localbuf.c */
 174 extern BufferDesc *LocalBufferDescriptors;
 175
 176 /* event counters in buf_init.c */
 177 extern long int ReadBufferCount;
 178 extern long int ReadLocalBufferCount;
 179 extern long int BufferHitCount;
 180 extern long int LocalBufferHitCount;
 181 extern long int BufferFlushCount;
 182 extern long int LocalBufferFlushCount;
 183 extern long int BufFileReadCount;
 184 extern long int BufFileWriteCount;
 185
 186
 187 /*
 188  * Internal routines: only called by bufmgr
 189  */
 190
 191 /* freelist.c */
 192 extern volatile BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy,
 193                                   bool *lock_held);
 194 extern void StrategyFreeBuffer(volatile BufferDesc *buf);
 195 extern bool StrategyRejectBuffer(BufferAccessStrategy strategy,
 196                                          volatile BufferDesc *buf);
 197
 198 extern int      StrategySyncStart(uint32 *complete_passes, uint32 *num_buf_alloc);
 199 extern Size StrategyShmemSize(void);
 200 extern void StrategyInitialize(bool init);
 201
 202 /* buf_table.c */
 203 extern Size BufTableShmemSize(int size);
 204 extern void InitBufTable(int size);
 205 extern uint32 BufTableHashCode(BufferTag *tagPtr);
 206 extern int      BufTableLookup(BufferTag *tagPtr, uint32 hashcode);
 207 extern int      BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id);
 208 extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode);
 209
 210 /* localbuf.c */
 211 extern BufferDesc *LocalBufferAlloc(SMgrRelation reln, ForkNumber forkNum,
 212                                  BlockNumber blockNum, bool *foundPtr);
 213 extern void MarkLocalBufferDirty(Buffer buffer);
 214 extern void DropRelFileNodeLocalBuffers(RelFileNode rnode, ForkNumber forkNum,
 215                                                         BlockNumber firstDelBlock);
 216 extern void AtEOXact_LocalBuffers(bool isCommit);
 217
 218 #endif   /* BUFMGR_INTERNALS_H */