*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.15 1998/01/07 21:02:21 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.16 1998/07/21 06:17:13 vadim Exp $
*
*-------------------------------------------------------------------------
*/
*/
int OidGenLockId;
+VariableCache ShmemVariableCache = NULL;
+
/* ----------------------------------------------------------------
* variable relation query/update routines
* ----------------------------------------------------------------
* In the version 2 transaction system, transaction id's are
* restricted in several ways.
*
- * First, all transaction id's are even numbers (4, 88, 121342, etc).
- * This means the binary representation of the number will never
- * have the least significent bit set. This bit is reserved to
- * indicate that the transaction id does not in fact hold an XID,
- * but rather a commit time. This makes it possible for the
- * vaccuum daemon to disgard information from the log and time
- * relations for committed tuples. This is important when archiving
- * tuples to an optical disk because tuples with commit times
- * stored in their xid fields will not need to consult the log
- * and time relations.
+ * -- Old comments removed --
*
* Second, since we may someday preform compression of the data
* in the log and time relations, we cause the numbering of the
* transaction id's 0 - 510 will never be used. This space is
* in fact used to store the version number of the postgres
* transaction log and will someday store compression information
- * about the log.
- *
- * Lastly, rather then access the variable relation each time
- * a backend requests a new transction id, we "prefetch" 32
- * transaction id's by incrementing the nextXid stored in the
- * var relation by 64 (remember only even xid's are legal) and then
- * returning these id's one at a time until they are exhausted.
- * This means we reduce the number of accesses to the variable
- * relation by 32 for each backend.
- *
- * Note: 32 has no special significance. We don't want the
- * number to be too large because if when the backend
- * terminates, we lose the xid's we cached.
+ * about the log. -- this is also old comments...
*
* ----------------
*/
-#define VAR_XID_PREFETCH 32
-
-static int prefetched_xid_count = 0;
-static TransactionId next_prefetched_xid;
+#define VAR_XID_PREFETCH 1024
void
GetNewTransactionId(TransactionId *xid)
{
- TransactionId nextid;
/* ----------------
* during bootstrap initialization, we return the special
return;
}
- /* ----------------
- * if we run out of prefetched xids, then we get some
- * more before handing them out to the caller.
- * ----------------
- */
-
- if (prefetched_xid_count == 0)
+ SpinAcquire(OidGenLockId); /* not good for concurrency... */
+
+ if (ShmemVariableCache->xid_count == 0)
{
- /* ----------------
- * obtain exclusive access to the variable relation page
- *
- * get the "next" xid from the variable relation
- * and save it in the prefetched id.
- * ----------------
- */
- SpinAcquire(OidGenLockId);
+ TransactionId nextid;
+
VariableRelationGetNextXid(&nextid);
- TransactionIdStore(nextid, &next_prefetched_xid);
-
- /* ----------------
- * now increment the variable relation's next xid
- * and reset the prefetched_xid_count. We multiply
- * the id by two because our xid's are always even.
- * ----------------
- */
- prefetched_xid_count = VAR_XID_PREFETCH;
- TransactionIdAdd(&nextid, prefetched_xid_count);
+ TransactionIdStore(nextid, &(ShmemVariableCache->nextXid));
+ ShmemVariableCache->xid_count = VAR_XID_PREFETCH;
+ TransactionIdAdd(&nextid, VAR_XID_PREFETCH);
VariableRelationPutNextXid(nextid);
- SpinRelease(OidGenLockId);
}
- /* ----------------
- * return the next prefetched xid in the pointer passed by
- * the user and decrement the prefetch count. We add two
- * to id we return the next time this is called because our
- * transaction ids are always even.
- *
- * XXX Transaction Ids used to be even as the low order bit was
- * used to determine commit status. This is no long true so
- * we now use even and odd transaction ids. -mer 5/26/92
- * ----------------
- */
- TransactionIdStore(next_prefetched_xid, xid);
- TransactionIdAdd(&next_prefetched_xid, 1);
- prefetched_xid_count--;
+ TransactionIdStore(ShmemVariableCache->nextXid, xid);
+ TransactionIdAdd(&(ShmemVariableCache->nextXid), 1);
+ (ShmemVariableCache->xid_count)--;
+
+ SpinRelease(OidGenLockId);
}
/* ----------------------------------------------------------------
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.27 1998/06/30 19:09:57 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.28 1998/07/21 06:17:35 vadim Exp $
*
*-------------------------------------------------------------------------
*/
#include "storage/proc.h"
#include "utils/dynahash.h"
#include "utils/hsearch.h"
+#include "utils/memutils.h"
+#include "access/transam.h"
/* shared memory global variables */
static unsigned long ShmemEnd = 0;
static unsigned long ShmemSize = 0; /* current size (and default) */
+extern VariableCache ShmemVariableCache; /* varsup.c */
+
SPINLOCK ShmemLock; /* lock for shared memory allocation */
SPINLOCK ShmemIndexLock; /* lock for shmem index access */
item;
bool found;
IpcMemoryId shmid;
-
/* if zero key, use default memory size */
if (size)
ShmemSize = size;
ShmemFreeStart = (unsigned long *) ShmemBase;
/* next is a shmem pointer to the shmem index */
ShmemIndexOffset = ShmemFreeStart + 1;
+ /* next is ShmemVariableCache */
+ ShmemVariableCache = (VariableCache) (ShmemIndexOffset + 1);
currFreeSpace +=
- sizeof(ShmemFreeStart) + sizeof(ShmemIndexOffset);
+ sizeof(ShmemFreeStart) + sizeof(ShmemIndexOffset) +
+ LONGALIGN(sizeof(VariableCacheData));
/*
* bootstrap initialize spin locks so we can start to use the
* setup the global free space count
*/
if (ShmemBootstrap)
+ {
*ShmemFreeStart = currFreeSpace;
+ memset (ShmemVariableCache, 0, sizeof(*ShmemVariableCache));
+ }
/* if ShmemFreeStart is NULL, then the allocator won't work */
Assert(*ShmemFreeStart);
OSDN Git Service
