src/backend/access/transam/varsup.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * varsup.c
   4  *        postgres OID & XID variables support routines
   5  *
   6  * Copyright (c) 2000, PostgreSQL Global Development Group
   7  *
   8  * IDENTIFICATION
   9  *        $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.38 2001/03/22 03:59:17 momjian Exp $
  10  *
  11  *-------------------------------------------------------------------------
  12  */
  13
  14 #include "postgres.h"
  15
  16 #include "access/transam.h"
  17 #include "access/xlog.h"
  18 #include "storage/proc.h"
  19
  20
  21 /* Number of XIDs and OIDs to prefetch (preallocate) per XLOG write */
  22 #define VAR_XID_PREFETCH                1024
  23 #define VAR_OID_PREFETCH                8192
  24
  25 /* Spinlocks for serializing generation of XIDs and OIDs, respectively */
  26 SPINLOCK        XidGenLockId;
  27 SPINLOCK        OidGenLockId;
  28
  29 /* pointer to "variable cache" in shared memory (set up by shmem.c) */
  30 VariableCache ShmemVariableCache = NULL;
  31
  32 void
  33 GetNewTransactionId(TransactionId *xid)
  34 {
  35
  36         /*
  37          * During bootstrap initialization, we return the special bootstrap
  38          * transaction id.
  39          */
  40         if (AMI_OVERRIDE)
  41         {
  42                 *xid = AmiTransactionId;
  43                 return;
  44         }
  45
  46         SpinAcquire(XidGenLockId);
  47
  48         *xid = ShmemVariableCache->nextXid;
  49
  50         (ShmemVariableCache->nextXid)++;
  51
  52         SpinRelease(XidGenLockId);
  53
  54         if (MyProc != (PROC *) NULL)
  55                 MyProc->xid = *xid;
  56 }
  57
  58 /*
  59  * Read nextXid but don't allocate it.
  60  */
  61 void
  62 ReadNewTransactionId(TransactionId *xid)
  63 {
  64
  65         /*
  66          * During bootstrap initialization, we return the special bootstrap
  67          * transaction id.
  68          */
  69         if (AMI_OVERRIDE)
  70         {
  71                 *xid = AmiTransactionId;
  72                 return;
  73         }
  74
  75         SpinAcquire(XidGenLockId);
  76         *xid = ShmemVariableCache->nextXid;
  77         SpinRelease(XidGenLockId);
  78 }
  79
  80 /* ----------------------------------------------------------------
  81  *                                      object id generation support
  82  * ----------------------------------------------------------------
  83  */
  84
  85 static Oid      lastSeenOid = InvalidOid;
  86
  87 void
  88 GetNewObjectId(Oid *oid_return)
  89 {
  90         SpinAcquire(OidGenLockId);
  91
  92         /* If we run out of logged for use oids then we must log more */
  93         if (ShmemVariableCache->oidCount == 0)
  94         {
  95                 XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
  96                 ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
  97         }
  98
  99         if (PointerIsValid(oid_return))
 100                 lastSeenOid = (*oid_return) = ShmemVariableCache->nextOid;
 101
 102         (ShmemVariableCache->nextOid)++;
 103         (ShmemVariableCache->oidCount)--;
 104
 105         SpinRelease(OidGenLockId);
 106 }
 107
 108 void
 109 CheckMaxObjectId(Oid assigned_oid)
 110 {
 111         if (lastSeenOid != InvalidOid && assigned_oid < lastSeenOid)
 112                 return;
 113
 114         SpinAcquire(OidGenLockId);
 115
 116         if (assigned_oid < ShmemVariableCache->nextOid)
 117         {
 118                 lastSeenOid = ShmemVariableCache->nextOid - 1;
 119                 SpinRelease(OidGenLockId);
 120                 return;
 121         }
 122
 123         /* If we are in the logged oid range, just bump nextOid up */
 124         if (assigned_oid <= ShmemVariableCache->nextOid +
 125                 ShmemVariableCache->oidCount - 1)
 126         {
 127                 ShmemVariableCache->oidCount -=
 128                         assigned_oid - ShmemVariableCache->nextOid + 1;
 129                 ShmemVariableCache->nextOid = assigned_oid + 1;
 130                 SpinRelease(OidGenLockId);
 131                 return;
 132         }
 133
 134         /*
 135          * We have exceeded the logged oid range. We should lock the database
 136          * and kill all other backends but we are loading oid's that we can
 137          * not guarantee are unique anyway, so we must rely on the user.
 138          */
 139
 140         XLogPutNextOid(assigned_oid + VAR_OID_PREFETCH);
 141         ShmemVariableCache->oidCount = VAR_OID_PREFETCH - 1;
 142         ShmemVariableCache->nextOid = assigned_oid + 1;
 143
 144         SpinRelease(OidGenLockId);
 145 }