granicus.if.org Git - postgresql/blob - 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 1.37 2001/03/18 20:18:59 tgl 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          * During bootstrap initialization, we return the special
  37          * bootstrap transaction id.
  38          */
  39         if (AMI_OVERRIDE)
  40         {
  41                 *xid = AmiTransactionId;
  42                 return;
  43         }
  44
  45         SpinAcquire(XidGenLockId);
  46
  47         *xid = ShmemVariableCache->nextXid;
  48
  49         (ShmemVariableCache->nextXid)++;
  50
  51         SpinRelease(XidGenLockId);
  52
  53         if (MyProc != (PROC *) NULL)
  54                 MyProc->xid = *xid;
  55 }
  56
  57 /*
  58  * Read nextXid but don't allocate it.
  59  */
  60 void
  61 ReadNewTransactionId(TransactionId *xid)
  62 {
  63         /*
  64          * During bootstrap initialization, we return the special
  65          * bootstrap transaction id.
  66          */
  67         if (AMI_OVERRIDE)
  68         {
  69                 *xid = AmiTransactionId;
  70                 return;
  71         }
  72
  73         SpinAcquire(XidGenLockId);
  74         *xid = ShmemVariableCache->nextXid;
  75         SpinRelease(XidGenLockId);
  76 }
  77
  78 /* ----------------------------------------------------------------
  79  *                                      object id generation support
  80  * ----------------------------------------------------------------
  81  */
  82
  83 static Oid lastSeenOid = InvalidOid;
  84
  85 void
  86 GetNewObjectId(Oid *oid_return)
  87 {
  88         SpinAcquire(OidGenLockId);
  89
  90         /* If we run out of logged for use oids then we must log more */
  91         if (ShmemVariableCache->oidCount == 0)
  92         {
  93                 XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
  94                 ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
  95         }
  96
  97         if (PointerIsValid(oid_return))
  98                 lastSeenOid = (*oid_return) = ShmemVariableCache->nextOid;
  99
 100         (ShmemVariableCache->nextOid)++;
 101         (ShmemVariableCache->oidCount)--;
 102
 103         SpinRelease(OidGenLockId);
 104 }
 105
 106 void
 107 CheckMaxObjectId(Oid assigned_oid)
 108 {
 109         if (lastSeenOid != InvalidOid && assigned_oid < lastSeenOid)
 110                 return;
 111
 112         SpinAcquire(OidGenLockId);
 113
 114         if (assigned_oid < ShmemVariableCache->nextOid)
 115         {
 116                 lastSeenOid = ShmemVariableCache->nextOid - 1;
 117                 SpinRelease(OidGenLockId);
 118                 return;
 119         }
 120
 121         /* If we are in the logged oid range, just bump nextOid up */
 122         if (assigned_oid <= ShmemVariableCache->nextOid +
 123                                                 ShmemVariableCache->oidCount - 1)
 124         {
 125                 ShmemVariableCache->oidCount -=
 126                         assigned_oid - ShmemVariableCache->nextOid + 1;
 127                 ShmemVariableCache->nextOid = assigned_oid + 1;
 128                 SpinRelease(OidGenLockId);
 129                 return;
 130         }
 131
 132         /*
 133          * We have exceeded the logged oid range.
 134          * We should lock the database and kill all other backends
 135          * but we are loading oid's that we can not guarantee are unique
 136          * anyway, so we must rely on the user.
 137          */
 138
 139         XLogPutNextOid(assigned_oid + VAR_OID_PREFETCH);
 140         ShmemVariableCache->oidCount = VAR_OID_PREFETCH - 1;
 141         ShmemVariableCache->nextOid = assigned_oid + 1;
 142
 143         SpinRelease(OidGenLockId);
 144 }