From fdaf44862beba24c12434d31df556fab25fd3ee7 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 14 Feb 2013 20:35:08 -0500
Subject: [PATCH] Invent pre-commit/pre-prepare/pre-subcommit events for xact
callbacks.
Currently it's only possible for loadable modules to get control during
post-commit cleanup of a transaction. That doesn't work too well if they
want to do something that could throw an error; for example, an FDW might
need to issue a remote commit, which could well fail. To improve matters,
extend the existing APIs for XactCallback and SubXactCallback functions
to provide new pre-commit events for this purpose.
The release notes will need to mention that existing callback functions
should be checked to make sure they don't do something unwanted when one
of the new event types occurs. In the examples within our source tree,
contrib/sepgsql was fine but plpgsql had been a bit too cute.
---
src/backend/access/transam/xact.c | 10 +++++++++-
src/include/access/xact.h | 7 +++++--
src/pl/plpgsql/src/pl_exec.c | 26 +++++++++++++-------------
3 files changed, 27 insertions(+), 16 deletions(-)
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 81d26874956..9a9724574be 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1825,6 +1825,8 @@ CommitTransaction(void)
break;
}
+ CallXactCallbacks(XACT_EVENT_PRE_COMMIT);
+
/*
* The remaining actions cannot call any user-defined code, so it's safe
* to start shutting down within-transaction services. But note that most
@@ -2028,6 +2030,8 @@ PrepareTransaction(void)
break;
}
+ CallXactCallbacks(XACT_EVENT_PRE_PREPARE);
+
/*
* The remaining actions cannot call any user-defined code, so it's safe
* to start shutting down within-transaction services. But note that most
@@ -4058,8 +4062,12 @@ CommitSubTransaction(void)
elog(WARNING, "CommitSubTransaction while in %s state",
TransStateAsString(s->state));
- /* Pre-commit processing goes here -- nothing to do at the moment */
+ /* Pre-commit processing goes here */
+
+ CallSubXactCallbacks(SUBXACT_EVENT_PRE_COMMIT_SUB, s->subTransactionId,
+ s->parent->subTransactionId);
+ /* Do the actual "commit", such as it is */
s->state = TRANS_COMMIT;
/* Must CCI to ensure commands of subtransaction are seen as done */
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index fcdff932721..8cadc549716 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -76,7 +76,9 @@ typedef enum
{
XACT_EVENT_COMMIT,
XACT_EVENT_ABORT,
- XACT_EVENT_PREPARE
+ XACT_EVENT_PREPARE,
+ XACT_EVENT_PRE_COMMIT,
+ XACT_EVENT_PRE_PREPARE
} XactEvent;
typedef void (*XactCallback) (XactEvent event, void *arg);
@@ -85,7 +87,8 @@ typedef enum
{
SUBXACT_EVENT_START_SUB,
SUBXACT_EVENT_COMMIT_SUB,
- SUBXACT_EVENT_ABORT_SUB
+ SUBXACT_EVENT_ABORT_SUB,
+ SUBXACT_EVENT_PRE_COMMIT_SUB
} SubXactEvent;
typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 591a432f542..70e67d9eb70 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -6150,7 +6150,7 @@ plpgsql_xact_cb(XactEvent event, void *arg)
* expect the regular abort recovery procedures to release everything of
* interest.
*/
- if (event != XACT_EVENT_ABORT)
+ if (event == XACT_EVENT_COMMIT || event == XACT_EVENT_PREPARE)
{
/* Shouldn't be any econtext stack entries left at commit */
Assert(simple_econtext_stack == NULL);
@@ -6159,7 +6159,7 @@ plpgsql_xact_cb(XactEvent event, void *arg)
FreeExecutorState(simple_eval_estate);
simple_eval_estate = NULL;
}
- else
+ else if (event == XACT_EVENT_ABORT)
{
simple_econtext_stack = NULL;
simple_eval_estate = NULL;
@@ -6178,19 +6178,19 @@ void
plpgsql_subxact_cb(SubXactEvent event, SubTransactionId mySubid,
SubTransactionId parentSubid, void *arg)
{
- if (event == SUBXACT_EVENT_START_SUB)
- return;
-
- while (simple_econtext_stack != NULL &&
- simple_econtext_stack->xact_subxid == mySubid)
+ if (event == SUBXACT_EVENT_COMMIT_SUB || event == SUBXACT_EVENT_ABORT_SUB)
{
- SimpleEcontextStackEntry *next;
+ while (simple_econtext_stack != NULL &&
+ simple_econtext_stack->xact_subxid == mySubid)
+ {
+ SimpleEcontextStackEntry *next;
- FreeExprContext(simple_econtext_stack->stack_econtext,
- (event == SUBXACT_EVENT_COMMIT_SUB));
- next = simple_econtext_stack->next;
- pfree(simple_econtext_stack);
- simple_econtext_stack = next;
+ FreeExprContext(simple_econtext_stack->stack_econtext,
+ (event == SUBXACT_EVENT_COMMIT_SUB));
+ next = simple_econtext_stack->next;
+ pfree(simple_econtext_stack);
+ simple_econtext_stack = next;
+ }
}
}
--
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