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Restructure subtransaction handling to reduce resource consumption,

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as per recent discussions.  Invent SubTransactionIds that are managed like
CommandIds (ie, counter is reset at start of each top transaction), and
use these instead of TransactionIds to keep track of subtransaction status
in those modules that need it.  This means that a subtransaction does not
need an XID unless it actually inserts/modifies rows in the database.
Accordingly, don't assign it an XID nor take a lock on the XID until it
tries to do that.  This saves a lot of overhead for subtransactions that
are only used for error recovery (eg plpgsql exceptions).  Also, arrange
to release a subtransaction's XID lock as soon as the subtransaction
exits, in both the commit and abort cases.  This avoids holding many
unique locks after a long series of subtransactions.  The price is some
additional overhead in XactLockTableWait, but that seems acceptable.
Finally, restructure the state machine in xact.c to have a more orthogonal
set of states for subtransactions.
This commit is contained in:
Tom Lane
2004-09-16 16:58:44 +00:00
parent 42c0d1f3cd
commit 8f9f198603
34 changed files with 1220 additions and 945 deletions
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25
src/backend/storage/file/fd.c
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.112 2004/08/29 05:06:47 momjian Exp $
* $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.113 2004/09/16 16:58:32 tgl Exp $
*
* NOTES:
*
@ -123,7 +123,7 @@ typedef struct vfd
{
signed short fd; /* current FD, or VFD_CLOSED if none */
unsigned short fdstate; /* bitflags for VFD's state */
TransactionId create_xid; /* for XACT_TEMPORARY fds, creating Xid */
SubTransactionId create_subid; /* for TEMPORARY fds, creating subxact */
File nextFree; /* link to next free VFD, if in freelist */
File lruMoreRecently; /* doubly linked recency-of-use list */
File lruLessRecently;
@ -171,7 +171,7 @@ typedef struct
FILE *file;
DIR *dir;
} desc;
TransactionId create_xid;
SubTransactionId create_subid;
} AllocateDesc;
static int numAllocatedDescs = 0;
@ -887,7 +887,7 @@ OpenTemporaryFile(bool interXact)
if (!interXact)
{
VfdCache[file].fdstate |= FD_XACT_TEMPORARY;
VfdCache[file].create_xid = GetCurrentTransactionId();
VfdCache[file].create_subid = GetCurrentSubTransactionId();
}
return file;
@ -1166,7 +1166,7 @@ TryAgain:
desc->kind = AllocateDescFile;
desc->desc.file = file;
desc->create_xid = GetCurrentTransactionId();
desc->create_subid = GetCurrentSubTransactionId();
numAllocatedDescs++;
return desc->desc.file;
}
@ -1281,7 +1281,7 @@ TryAgain:
desc->kind = AllocateDescDir;
desc->desc.dir = dir;
desc->create_xid = GetCurrentTransactionId();
desc->create_subid = GetCurrentSubTransactionId();
numAllocatedDescs++;
return desc->desc.dir;
}
@ -1359,10 +1359,11 @@ closeAllVfds(void)
*
* Take care of subtransaction commit/abort. At abort, we close temp files
* that the subtransaction may have opened. At commit, we reassign the
* files that were opened to the parent transaction.
* files that were opened to the parent subtransaction.
*/
void
AtEOSubXact_Files(bool isCommit, TransactionId myXid, TransactionId parentXid)
AtEOSubXact_Files(bool isCommit, SubTransactionId mySubid,
SubTransactionId parentSubid)
{
Index i;
@ -1374,10 +1375,10 @@ AtEOSubXact_Files(bool isCommit, TransactionId myXid, TransactionId parentXid)
unsigned short fdstate = VfdCache[i].fdstate;
if ((fdstate & FD_XACT_TEMPORARY) &&
VfdCache[i].create_xid == myXid)
VfdCache[i].create_subid == mySubid)
{
if (isCommit)
VfdCache[i].create_xid = parentXid;
VfdCache[i].create_subid = parentSubid;
else if (VfdCache[i].fileName != NULL)
FileClose(i);
}
@ -1386,10 +1387,10 @@ AtEOSubXact_Files(bool isCommit, TransactionId myXid, TransactionId parentXid)
for (i = 0; i < numAllocatedDescs; i++)
{
if (allocatedDescs[i].create_xid == myXid)
if (allocatedDescs[i].create_subid == mySubid)
{
if (isCommit)
allocatedDescs[i].create_xid = parentXid;
allocatedDescs[i].create_subid = parentSubid;
else
{
/* have to recheck the item after FreeDesc (ugly) */