On 6/27/18 18:51, Peter Eisentraut wrote:
> On 6/27/18 17:44, Andres Freund wrote:
>> This hasn't progressed in a while. Peter, since you committed the
>> relevant change, could you update us please?
>
> I've been on vacation for a bit. I will work on this next. I hope to
> have a solution in a few days.
Proposed patch attached.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 95fc7156afe521b715fab08d44606774df875e92 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pete...@gmx.net>
Date: Fri, 29 Jun 2018 13:28:39 +0200
Subject: [PATCH] Fix assert in nested SQL procedure call
When executing CALL in PL/pgSQL, we need to set a snapshot before
invoking the to-be-called procedure. Otherwise, the to-be-called
procedure might end up running without a snapshot. For LANGUAGE SQL
procedures, this would result in an assertion failure. (For most other
languages, this is usually not a problem, because those use SPI and SPI
sets snapshots in most cases.) Setting the snapshot restores the
behavior of how CALL worked when it was handled as a generic SQL
statement in PL/pgSQL (exec_stmt_execsql()).
This change revealed another problem: In SPI_commit(), we popped the
active snapshot before committing the transaction, to avoid "snapshot %p
still active" errors. However, there is no particular reason why only
at most one snapshot should be on the stack. So change this to pop all
active snapshots instead of only one.
---
src/backend/executor/spi.c | 7 +++-
.../src/expected/plpgsql_transaction.out | 19 +++++++++++
src/pl/plpgsql/src/pl_exec.c | 32 ++++++++++++++++---
.../plpgsql/src/sql/plpgsql_transaction.sql | 20 ++++++++++++
4 files changed, 72 insertions(+), 6 deletions(-)
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 22dd55c378..5756365c8f 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -228,8 +228,13 @@ SPI_commit(void)
_SPI_current->internal_xact = true;
- if (ActiveSnapshotSet())
+ /*
+ * Before committing, pop all active snapshots to avoid error about
+ * "snapshot %p still active".
+ */
+ while (ActiveSnapshotSet())
PopActiveSnapshot();
+
CommitTransactionCommand();
MemoryContextSwitchTo(oldcontext);
diff --git a/src/pl/plpgsql/src/expected/plpgsql_transaction.out
b/src/pl/plpgsql/src/expected/plpgsql_transaction.out
index 7f008ac57e..274b2c6f17 100644
--- a/src/pl/plpgsql/src/expected/plpgsql_transaction.out
+++ b/src/pl/plpgsql/src/expected/plpgsql_transaction.out
@@ -432,6 +432,25 @@ END;
$$;
ERROR: EXECUTE of transaction commands is not implemented
CONTEXT: PL/pgSQL function inline_code_block line 3 at EXECUTE
+-- snapshot handling test
+TRUNCATE test2;
+CREATE PROCEDURE transaction_test9()
+LANGUAGE SQL
+AS $$
+INSERT INTO test2 VALUES (42);
+$$;
+DO LANGUAGE plpgsql $$
+BEGIN
+ ROLLBACK;
+ CALL transaction_test9();
+END
+$$;
+SELECT * FROM test2;
+ x
+----
+ 42
+(1 row)
+
DROP TABLE test1;
DROP TABLE test2;
DROP TABLE test3;
diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 66ecf5eb55..e39f7357bd 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -2075,6 +2075,7 @@ exec_stmt_call(PLpgSQL_execstate *estate,
PLpgSQL_stmt_call *stmt)
ParamListInfo paramLI;
LocalTransactionId before_lxid;
LocalTransactionId after_lxid;
+ bool pushed_active_snap = false;
int rc;
if (expr->plan == NULL)
@@ -2090,6 +2091,7 @@ exec_stmt_call(PLpgSQL_execstate *estate,
PLpgSQL_stmt_call *stmt)
/*
* The procedure call could end transactions, which would upset
the
* snapshot management in SPI_execute*, so don't let it do it.
+ * Instead, we set the snapshots ourselves below.
*/
expr->plan->no_snapshots = true;
}
@@ -2098,6 +2100,16 @@ exec_stmt_call(PLpgSQL_execstate *estate,
PLpgSQL_stmt_call *stmt)
before_lxid = MyProc->lxid;
+ /*
+ * Set snapshot only for non-read-only procedures, similar to SPI
+ * behavior.
+ */
+ if (!estate->readonly_func)
+ {
+ PushActiveSnapshot(GetTransactionSnapshot());
+ pushed_active_snap = true;
+ }
+
PG_TRY();
{
rc = SPI_execute_plan_with_paramlist(expr->plan, paramLI,
@@ -2126,12 +2138,22 @@ exec_stmt_call(PLpgSQL_execstate *estate,
PLpgSQL_stmt_call *stmt)
elog(ERROR, "SPI_execute_plan_with_paramlist failed executing
query \"%s\": %s",
expr->query, SPI_result_code_string(rc));
- /*
- * If we are in a new transaction after the call, we need to reset some
- * internal state.
- */
- if (before_lxid != after_lxid)
+ if (before_lxid == after_lxid)
+ {
+ /*
+ * If we are still in the same transaction after the call, pop
the
+ * snapshot that we might have pushed. (If it's a new
transaction,
+ * then all the snapshots are gone already.)
+ */
+ if (pushed_active_snap)
+ PopActiveSnapshot();
+ }
+ else
{
+ /*
+ * If we are in a new transaction after the call, we need to
reset
+ * some internal state.
+ */
estate->simple_eval_estate = NULL;
plpgsql_create_econtext(estate);
}
diff --git a/src/pl/plpgsql/src/sql/plpgsql_transaction.sql
b/src/pl/plpgsql/src/sql/plpgsql_transaction.sql
index eddc518bb6..1624aed6ec 100644
--- a/src/pl/plpgsql/src/sql/plpgsql_transaction.sql
+++ b/src/pl/plpgsql/src/sql/plpgsql_transaction.sql
@@ -354,6 +354,26 @@ CREATE TABLE test2 (x int);
END;
$$;
+
+-- snapshot handling test
+TRUNCATE test2;
+
+CREATE PROCEDURE transaction_test9()
+LANGUAGE SQL
+AS $$
+INSERT INTO test2 VALUES (42);
+$$;
+
+DO LANGUAGE plpgsql $$
+BEGIN
+ ROLLBACK;
+ CALL transaction_test9();
+END
+$$;
+
+SELECT * FROM test2;
+
+
DROP TABLE test1;
DROP TABLE test2;
DROP TABLE test3;
--
2.18.0
