From 6f59777c65d557485e933a383ebc4c3fdfc1a2b7 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Sat, 22 Jan 2011 20:51:32 -0500
Subject: [PATCH] Code cleanup for assign_transaction_read_only.
As in commit fb4c5d2798730f60b102d775f22fb53c26a6445d on 2011-01-21,
this avoids spurious debug messages and allows idempotent changes at
any time. Along the way, make assign_XactIsoLevel allow idempotent
changes even when not within a subtransaction, to be consistent with
the new coding of assign_transaction_read_only and because there's
no compelling reason to do otherwise.
Kevin Grittner, with some adjustments.
---
src/backend/commands/variable.c | 53 ++++++++++++++-
src/backend/utils/misc/guc.c | 29 ---------
src/include/commands/variable.h | 2 +
src/test/regress/expected/transactions.out | 75 ++++++++++++++++++++++
src/test/regress/sql/transactions.sql | 42 ++++++++++++
5 files changed, 170 insertions(+), 31 deletions(-)
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 1e9bdc3f218..139148eec2e 100644
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -543,14 +543,63 @@ show_log_timezone(void)
}
+/*
+ * SET TRANSACTION READ ONLY and SET TRANSACTION READ WRITE
+ *
+ * We allow idempotent changes (r/w -> r/w and r/o -> r/o) at any time, and
+ * we also always allow changes from read-write to read-only. However,
+ * read-only to read-write may be changed only when source == PGC_S_OVERRIDE
+ * (i.e. we're aborting a read only transaction and restoring the previous
+ * setting) or in a top-level transaction that has not yet taken an initial
+ * snapshot.
+ */
+bool
+assign_transaction_read_only(bool newval, bool doit, GucSource source)
+{
+ if (source != PGC_S_OVERRIDE && newval == false && XactReadOnly)
+ {
+ /* Can't go to r/w mode inside a r/o transaction */
+ if (IsSubTransaction())
+ {
+ ereport(GUC_complaint_elevel(source),
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("cannot set transaction read-write mode inside a read-only transaction")));
+ return false;
+ }
+ /* Top level transaction can't change to r/w after first snapshot. */
+ if (FirstSnapshotSet)
+ {
+ ereport(GUC_complaint_elevel(source),
+ (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
+ errmsg("transaction read-write mode must be set before any query")));
+ return false;
+ }
+ /* Can't go to r/w mode while recovery is still active */
+ if (RecoveryInProgress())
+ {
+ ereport(GUC_complaint_elevel(source),
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("cannot set transaction read-write mode during recovery")));
+ return false;
+ }
+ }
+
+ return true;
+}
+
/*
* SET TRANSACTION ISOLATION LEVEL
+ *
+ * We allow idempotent changes at any time, but otherwise this can only be
+ * changed from a toplevel transaction that has not yet taken a snapshot, or
+ * when source == PGC_S_OVERRIDE (i.e. we're aborting a transaction and
+ * restoring the previously set value).
*/
const char *
assign_XactIsoLevel(const char *value, bool doit, GucSource source)
{
/* source == PGC_S_OVERRIDE means do it anyway, eg at xact abort */
- if (source != PGC_S_OVERRIDE)
+ if (source != PGC_S_OVERRIDE && strcmp(value, XactIsoLevel_string) != 0)
{
if (FirstSnapshotSet)
{
@@ -560,7 +609,7 @@ assign_XactIsoLevel(const char *value, bool doit, GucSource source)
return NULL;
}
/* We ignore a subtransaction setting it to the existing value. */
- if (IsSubTransaction() && strcmp(value, XactIsoLevel_string) != 0)
+ if (IsSubTransaction())
{
ereport(GUC_complaint_elevel(source),
(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 73b9f1b01ca..2c95ef80c45 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -168,7 +168,6 @@ static bool assign_bonjour(bool newval, bool doit, GucSource source);
static bool assign_ssl(bool newval, bool doit, GucSource source);
static bool assign_stage_log_stats(bool newval, bool doit, GucSource source);
static bool assign_log_stats(bool newval, bool doit, GucSource source);
-static bool assign_transaction_read_only(bool newval, bool doit, GucSource source);
static const char *assign_canonical_path(const char *newval, bool doit, GucSource source);
static const char *assign_timezone_abbreviations(const char *newval, bool doit, GucSource source);
static const char *show_archive_command(void);
@@ -7843,34 +7842,6 @@ assign_log_stats(bool newval, bool doit, GucSource source)
return true;
}
-static bool
-assign_transaction_read_only(bool newval, bool doit, GucSource source)
-{
- /* Can't go to r/w mode inside a r/o transaction */
- if (newval == false && XactReadOnly && IsSubTransaction())
- {
- ereport(GUC_complaint_elevel(source),
- (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
- errmsg("cannot set transaction read-write mode inside a read-only transaction")));
- /* source == PGC_S_OVERRIDE means do it anyway, eg at xact abort */
- if (source != PGC_S_OVERRIDE)
- return false;
- }
-
- /* Can't go to r/w mode while recovery is still active */
- if (newval == false && XactReadOnly && RecoveryInProgress())
- {
- ereport(GUC_complaint_elevel(source),
- (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
- errmsg("cannot set transaction read-write mode during recovery")));
- /* source == PGC_S_OVERRIDE means do it anyway, eg at xact abort */
- if (source != PGC_S_OVERRIDE)
- return false;
- }
-
- return true;
-}
-
static const char *
assign_canonical_path(const char *newval, bool doit, GucSource source)
{
diff --git a/src/include/commands/variable.h b/src/include/commands/variable.h
index 7ac8ed8f9f7..2fc144e1e12 100644
--- a/src/include/commands/variable.h
+++ b/src/include/commands/variable.h
@@ -21,6 +21,8 @@ extern const char *show_timezone(void);
extern const char *assign_log_timezone(const char *value,
bool doit, GucSource source);
extern const char *show_log_timezone(void);
+extern bool assign_transaction_read_only(bool value,
+ bool doit, GucSource source);
extern const char *assign_XactIsoLevel(const char *value,
bool doit, GucSource source);
extern const char *show_XactIsoLevel(void);
diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index 84d14537f14..b91c9d8e237 100644
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -43,6 +43,81 @@ SELECT * FROM aggtest;
-- Read-only tests
CREATE TABLE writetest (a int);
CREATE TEMPORARY TABLE temptest (a int);
+BEGIN;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+SET TRANSACTION READ WRITE; --fail
+ERROR: transaction read-write mode must be set before any query
+COMMIT;
+BEGIN;
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+SAVEPOINT x;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; --fail
+ERROR: cannot set transaction read-write mode inside a read-only transaction
+COMMIT;
+BEGIN;
+SET TRANSACTION READ WRITE; -- ok
+SAVEPOINT x;
+SET TRANSACTION READ WRITE; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; --fail
+ERROR: cannot set transaction read-write mode inside a read-only transaction
+COMMIT;
+BEGIN;
+SET TRANSACTION READ WRITE; -- ok
+SAVEPOINT x;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+ROLLBACK TO SAVEPOINT x;
+SHOW transaction_read_only; -- off
+ transaction_read_only
+-----------------------
+ off
+(1 row)
+
+SAVEPOINT y;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ a
+---
+(0 rows)
+
+RELEASE SAVEPOINT y;
+SHOW transaction_read_only; -- off
+ transaction_read_only
+-----------------------
+ off
+(1 row)
+
+COMMIT;
SET SESSION CHARACTERISTICS AS TRANSACTION READ ONLY;
DROP TABLE writetest; -- fail
ERROR: cannot execute DROP TABLE in a read-only transaction
diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index 17e830e7a4c..7c9638f05e2 100644
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -39,6 +39,48 @@ SELECT * FROM aggtest;
CREATE TABLE writetest (a int);
CREATE TEMPORARY TABLE temptest (a int);
+BEGIN;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+SET TRANSACTION READ WRITE; --fail
+COMMIT;
+
+BEGIN;
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+SAVEPOINT x;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; --fail
+COMMIT;
+
+BEGIN;
+SET TRANSACTION READ WRITE; -- ok
+SAVEPOINT x;
+SET TRANSACTION READ WRITE; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+SET TRANSACTION READ ONLY; -- ok
+SET TRANSACTION READ WRITE; --fail
+COMMIT;
+
+BEGIN;
+SET TRANSACTION READ WRITE; -- ok
+SAVEPOINT x;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+ROLLBACK TO SAVEPOINT x;
+SHOW transaction_read_only; -- off
+SAVEPOINT y;
+SET TRANSACTION READ ONLY; -- ok
+SELECT * FROM writetest; -- ok
+RELEASE SAVEPOINT y;
+SHOW transaction_read_only; -- off
+COMMIT;
+
SET SESSION CHARACTERISTICS AS TRANSACTION READ ONLY;
DROP TABLE writetest; -- fail
--
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