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VariableCache (next XID generator) is placed in shmem.
This commit is contained in:
Vadim B. Mikheev
parent
224a62c5b7
commit
5afe171443
@ -7,7 +7,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.15 1998/01/07 21:02:21 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.16 1998/07/21 06:17:13 vadim Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -31,6 +31,8 @@ static void VariableRelationPutNextOid(Oid *oidP);
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*/
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int OidGenLockId;
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VariableCache ShmemVariableCache = NULL;
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/* ----------------------------------------------------------------
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* variable relation query/update routines
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* ----------------------------------------------------------------
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@ -258,16 +260,7 @@ VariableRelationPutNextOid(Oid *oidP)
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* In the version 2 transaction system, transaction id's are
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* restricted in several ways.
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*
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* First, all transaction id's are even numbers (4, 88, 121342, etc).
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* This means the binary representation of the number will never
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* have the least significent bit set. This bit is reserved to
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* indicate that the transaction id does not in fact hold an XID,
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* but rather a commit time. This makes it possible for the
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* vaccuum daemon to disgard information from the log and time
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* relations for committed tuples. This is important when archiving
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* tuples to an optical disk because tuples with commit times
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* stored in their xid fields will not need to consult the log
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* and time relations.
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* -- Old comments removed --
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*
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* Second, since we may someday preform compression of the data
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* in the log and time relations, we cause the numbering of the
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@ -276,32 +269,16 @@ VariableRelationPutNextOid(Oid *oidP)
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* transaction id's 0 - 510 will never be used. This space is
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* in fact used to store the version number of the postgres
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* transaction log and will someday store compression information
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* about the log.
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*
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* Lastly, rather then access the variable relation each time
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* a backend requests a new transction id, we "prefetch" 32
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* transaction id's by incrementing the nextXid stored in the
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* var relation by 64 (remember only even xid's are legal) and then
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* returning these id's one at a time until they are exhausted.
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* This means we reduce the number of accesses to the variable
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* relation by 32 for each backend.
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*
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* Note: 32 has no special significance. We don't want the
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* number to be too large because if when the backend
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* terminates, we lose the xid's we cached.
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* about the log. -- this is also old comments...
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*
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* ----------------
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*/
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#define VAR_XID_PREFETCH 32
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static int prefetched_xid_count = 0;
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static TransactionId next_prefetched_xid;
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#define VAR_XID_PREFETCH 1024
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void
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GetNewTransactionId(TransactionId *xid)
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{
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TransactionId nextid;
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/* ----------------
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* during bootstrap initialization, we return the special
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@ -314,51 +291,24 @@ GetNewTransactionId(TransactionId *xid)
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return;
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}
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/* ----------------
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* if we run out of prefetched xids, then we get some
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* more before handing them out to the caller.
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* ----------------
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*/
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if (prefetched_xid_count == 0)
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SpinAcquire(OidGenLockId); /* not good for concurrency... */
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if (ShmemVariableCache->xid_count == 0)
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{
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/* ----------------
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* obtain exclusive access to the variable relation page
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*
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* get the "next" xid from the variable relation
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* and save it in the prefetched id.
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* ----------------
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*/
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SpinAcquire(OidGenLockId);
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TransactionId nextid;
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VariableRelationGetNextXid(&nextid);
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TransactionIdStore(nextid, &next_prefetched_xid);
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/* ----------------
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* now increment the variable relation's next xid
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* and reset the prefetched_xid_count. We multiply
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* the id by two because our xid's are always even.
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* ----------------
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*/
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prefetched_xid_count = VAR_XID_PREFETCH;
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TransactionIdAdd(&nextid, prefetched_xid_count);
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TransactionIdStore(nextid, &(ShmemVariableCache->nextXid));
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ShmemVariableCache->xid_count = VAR_XID_PREFETCH;
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TransactionIdAdd(&nextid, VAR_XID_PREFETCH);
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VariableRelationPutNextXid(nextid);
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SpinRelease(OidGenLockId);
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}
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/* ----------------
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* return the next prefetched xid in the pointer passed by
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* the user and decrement the prefetch count. We add two
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* to id we return the next time this is called because our
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* transaction ids are always even.
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*
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* XXX Transaction Ids used to be even as the low order bit was
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* used to determine commit status. This is no long true so
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* we now use even and odd transaction ids. -mer 5/26/92
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* ----------------
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*/
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TransactionIdStore(next_prefetched_xid, xid);
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TransactionIdAdd(&next_prefetched_xid, 1);
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prefetched_xid_count--;
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TransactionIdStore(ShmemVariableCache->nextXid, xid);
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TransactionIdAdd(&(ShmemVariableCache->nextXid), 1);
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(ShmemVariableCache->xid_count)--;
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SpinRelease(OidGenLockId);
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}
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/* ----------------------------------------------------------------
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@ -7,7 +7,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.27 1998/06/30 19:09:57 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.28 1998/07/21 06:17:35 vadim Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -67,6 +67,8 @@
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#include "storage/proc.h"
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#include "utils/dynahash.h"
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#include "utils/hsearch.h"
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#include "utils/memutils.h"
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#include "access/transam.h"
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/* shared memory global variables */
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@ -74,6 +76,8 @@ unsigned long ShmemBase = 0; /* start and end address of shared memory */
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static unsigned long ShmemEnd = 0;
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static unsigned long ShmemSize = 0; /* current size (and default) */
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extern VariableCache ShmemVariableCache; /* varsup.c */
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SPINLOCK ShmemLock; /* lock for shared memory allocation */
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SPINLOCK ShmemIndexLock; /* lock for shmem index access */
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@ -151,7 +155,6 @@ InitShmem(unsigned int key, unsigned int size)
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item;
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bool found;
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IpcMemoryId shmid;
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/* if zero key, use default memory size */
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if (size)
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ShmemSize = size;
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@ -180,9 +183,12 @@ InitShmem(unsigned int key, unsigned int size)
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ShmemFreeStart = (unsigned long *) ShmemBase;
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/* next is a shmem pointer to the shmem index */
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ShmemIndexOffset = ShmemFreeStart + 1;
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/* next is ShmemVariableCache */
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ShmemVariableCache = (VariableCache) (ShmemIndexOffset + 1);
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currFreeSpace +=
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sizeof(ShmemFreeStart) + sizeof(ShmemIndexOffset);
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sizeof(ShmemFreeStart) + sizeof(ShmemIndexOffset) +
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LONGALIGN(sizeof(VariableCacheData));
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/*
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* bootstrap initialize spin locks so we can start to use the
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@ -196,7 +202,10 @@ InitShmem(unsigned int key, unsigned int size)
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* setup the global free space count
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*/
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if (ShmemBootstrap)
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{
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*ShmemFreeStart = currFreeSpace;
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memset (ShmemVariableCache, 0, sizeof(*ShmemVariableCache));
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}
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/* if ShmemFreeStart is NULL, then the allocator won't work */
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Assert(*ShmemFreeStart);
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@ -6,7 +6,7 @@
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*
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* Copyright (c) 1994, Regents of the University of California
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*
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* $Id: transam.h,v 1.14 1998/02/26 04:40:30 momjian Exp $
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* $Id: transam.h,v 1.15 1998/07/21 06:17:39 vadim Exp $
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*
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* NOTES
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* Transaction System Version 101 now support proper oid
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@ -114,6 +114,24 @@ typedef struct VariableRelationContentsData
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typedef VariableRelationContentsData *VariableRelationContents;
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/*
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* VariableCache is placed in shmem and used by backends to
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* get next available XID & OID without access to
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* variable relation. Actually, I would like to have two
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* different on-disk storages for next XID and OID...
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* But hoping that someday we will use per database OID
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* generator I leaved this as is. - vadim 07/21/98
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*/
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typedef struct VariableCacheData
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{
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uint32 xid_count;
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TransactionId nextXid;
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uint32 oid_count; /* not implemented, yet */
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Oid nextOid;
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} VariableCacheData;
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typedef VariableCacheData *VariableCache;
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/* ----------------
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* extern declarations
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* ----------------
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