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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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6
src/include/storage/large_object.h
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@@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/large_object.h,v 1.29 2004/08/29 04:13:10 momjian Exp $
* $PostgreSQL: pgsql/src/include/storage/large_object.h,v 1.30 2004/09/16 16:58:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -20,7 +20,7 @@
* Data about a currently-open large object.
*
* id is the logical OID of the large object
* xid is the transaction Id that opened the LO (or currently owns it)
* subid is the subtransaction that opened the LO (or currently owns it)
* offset is the current seek offset within the LO
* flags contains some flag bits
*
@@ -32,7 +32,7 @@
typedef struct LargeObjectDesc
{
Oid id; /* LO's identifier */
TransactionId xid; /* owning XID */
SubTransactionId subid; /* owning subtransaction ID */
uint32 offset; /* current seek pointer */
int flags; /* locking info, etc */