VariableCache (next XID generator) is placed in shmem.

This commit is contained in:
Vadim B. Mikheev 1998-07-21 06:17:39 +00:00
parent 224a62c5b7
commit 5afe171443
3 changed files with 50 additions and 73 deletions

View File

@ -7,7 +7,7 @@
*
*
* 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 $
*
*-------------------------------------------------------------------------
*/
@ -31,6 +31,8 @@ static void VariableRelationPutNextOid(Oid *oidP);
*/
int OidGenLockId;
VariableCache ShmemVariableCache = NULL;
/* ----------------------------------------------------------------
* variable relation query/update routines
* ----------------------------------------------------------------
@ -258,16 +260,7 @@ VariableRelationPutNextOid(Oid *oidP)
* 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
@ -276,32 +269,16 @@ VariableRelationPutNextOid(Oid *oidP)
* 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
@ -314,51 +291,24 @@ GetNewTransactionId(TransactionId *xid)
return;
}
/* ----------------
* if we run out of prefetched xids, then we get some
* more before handing them out to the caller.
* ----------------
*/
SpinAcquire(OidGenLockId); /* not good for concurrency... */
if (prefetched_xid_count == 0)
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);
VariableRelationGetNextXid(&nextid);
TransactionIdStore(nextid, &next_prefetched_xid);
TransactionId nextid;
/* ----------------
* 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);
VariableRelationGetNextXid(&nextid);
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);
}
/* ----------------------------------------------------------------

View File

@ -7,7 +7,7 @@
*
*
* 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 $
*
*-------------------------------------------------------------------------
*/
@ -67,6 +67,8 @@
#include "storage/proc.h"
#include "utils/dynahash.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"
#include "access/transam.h"
/* shared memory global variables */
@ -74,6 +76,8 @@ unsigned long ShmemBase = 0; /* start and end address of shared memory */
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 */
@ -151,7 +155,6 @@ InitShmem(unsigned int key, unsigned int size)
item;
bool found;
IpcMemoryId shmid;
/* if zero key, use default memory size */
if (size)
ShmemSize = size;
@ -180,9 +183,12 @@ InitShmem(unsigned int key, unsigned int 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
@ -196,7 +202,10 @@ InitShmem(unsigned int key, unsigned int size)
* 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);

View File

@ -6,7 +6,7 @@
*
* Copyright (c) 1994, Regents of the University of California
*
* $Id: transam.h,v 1.14 1998/02/26 04:40:30 momjian Exp $
* $Id: transam.h,v 1.15 1998/07/21 06:17:39 vadim Exp $
*
* NOTES
* Transaction System Version 101 now support proper oid
@ -114,6 +114,24 @@ typedef struct VariableRelationContentsData
typedef VariableRelationContentsData *VariableRelationContents;
/*
* VariableCache is placed in shmem and used by backends to
* get next available XID & OID without access to
* variable relation. Actually, I would like to have two
* different on-disk storages for next XID and OID...
* But hoping that someday we will use per database OID
* generator I leaved this as is. - vadim 07/21/98
*/
typedef struct VariableCacheData
{
uint32 xid_count;
TransactionId nextXid;
uint32 oid_count; /* not implemented, yet */
Oid nextOid;
} VariableCacheData;
typedef VariableCacheData *VariableCache;
/* ----------------
* extern declarations
* ----------------