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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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60
src/pl/plpgsql/src/pl_exec.c
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@@ -3,7 +3,7 @@
* procedural language
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.119 2004/09/13 20:09:20 tgl Exp $
* $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.120 2004/09/16 16:58:44 tgl Exp $
*
* This software is copyrighted by Jan Wieck - Hamburg.
*
@@ -4240,52 +4240,38 @@ exec_set_found(PLpgSQL_execstate *estate, bool state)
}
/*
* plpgsql_eoxact --- post-transaction-commit-or-abort cleanup
* plpgsql_xact_cb --- post-transaction-commit-or-abort cleanup
*
* If a simple_eval_estate was created in the current transaction,
* it has to be cleaned up, and we have to mark all active PLpgSQL_expr
* structs that are using it as no longer active.
*
* XXX Do we need to do anything at subtransaction events?
* Maybe subtransactions need to have their own simple_eval_estate?
* It would get a lot messier, so for now let's assume we don't need that.
*/
void
plpgsql_xact_cb(XactEvent event, TransactionId parentXid, void *arg)
plpgsql_xact_cb(XactEvent event, void *arg)
{
PLpgSQL_expr *expr;
PLpgSQL_expr *enext;
switch (event)
/* Mark all active exprs as inactive */
for (expr = active_simple_exprs; expr; expr = enext)
{
/*
* Nothing to do at subtransaction events
*
* XXX really? Maybe subtransactions need to have their own
* simple_eval_estate? It would get a lot messier, so for now
* let's assume we don't need that.
*/
case XACT_EVENT_START_SUB:
case XACT_EVENT_ABORT_SUB:
case XACT_EVENT_COMMIT_SUB:
break;
case XACT_EVENT_ABORT:
case XACT_EVENT_COMMIT:
/* Mark all active exprs as inactive */
for (expr = active_simple_exprs; expr; expr = enext)
{
enext = expr->expr_simple_next;
expr->expr_simple_state = NULL;
expr->expr_simple_next = NULL;
}
active_simple_exprs = NULL;
/*
* If we are doing a clean transaction shutdown, free the
* EState (so that any remaining resources will be released
* correctly). In an abort, we expect the regular abort
* recovery procedures to release everything of interest.
*/
if (event == XACT_EVENT_COMMIT && simple_eval_estate)
FreeExecutorState(simple_eval_estate);
simple_eval_estate = NULL;
break;
enext = expr->expr_simple_next;
expr->expr_simple_state = NULL;
expr->expr_simple_next = NULL;
}
active_simple_exprs = NULL;
/*
* If we are doing a clean transaction shutdown, free the
* EState (so that any remaining resources will be released
* correctly). In an abort, we expect the regular abort
* recovery procedures to release everything of interest.
*/
if (event == XACT_EVENT_COMMIT && simple_eval_estate)
FreeExecutorState(simple_eval_estate);
simple_eval_estate = NULL;
}

4
src/pl/plpgsql/src/plpgsql.h
View File

@@ -3,7 +3,7 @@
* procedural language
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.55 2004/09/14 23:46:46 neilc Exp $
* $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.56 2004/09/16 16:58:44 tgl Exp $
*
* This software is copyrighted by Jan Wieck - Hamburg.
*
@@ -708,7 +708,7 @@ extern Datum plpgsql_exec_function(PLpgSQL_function *func,
FunctionCallInfo fcinfo);
extern HeapTuple plpgsql_exec_trigger(PLpgSQL_function *func,
TriggerData *trigdata);
extern void plpgsql_xact_cb(XactEvent event, TransactionId parentXid, void *arg);
extern void plpgsql_xact_cb(XactEvent event, void *arg);
/* ----------
* Functions for the dynamic string handling in pl_funcs.c