I would like to allow RULEs ON INSERT, ON UPDATE and ON DELETE during
read only transactions iff they generate only SELECT statements that act
INSTEAD OF the actual event.
CREATE RULE foorah
AS ON INSERT TO foo
DO INSTEAD SELECT remote_insert(NEW.col1, NEW.col2, ...);
The above rule is currently disallowed during READ ONLY transactions,
even though the write action is re-written into a read-only action.
I have a small patch that allows this, attached here with test cases.
This would be a small, but useful additional feature for Hot Standby,
since it would allow INSERT, UPDATE, DELETE statements to be re-routed,
for various applications.
--
Simon Riggs www.2ndQuadrant.com
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 1383123..0210d35 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -581,6 +581,14 @@ ExecCheckXactReadOnly(PlannedStmt *plannedstmt)
if (plannedstmt->intoClause != NULL)
goto fail;
+ /*
+ * If we're running a SELECT, allow it. This ensures that a
+ * write rule such as ON INSERT DO SELECT can be executed in
+ * a read-only session.
+ */
+ if (plannedstmt->commandType == CMD_SELECT)
+ return;
+
/* Fail if write permissions are requested on any non-temp table */
foreach(l, plannedstmt->rtable)
{
diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index fc98f01..f9eda6b 100644
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -65,6 +65,24 @@ SELECT * FROM writetest, temptest; -- ok
CREATE TABLE test AS SELECT * FROM writetest; -- fail
ERROR: transaction is read-only
+BEGIN;
+SET transaction_read_only = false;
+CREATE RULE write2read_rule AS ON INSERT TO writetest DO INSTEAD SELECT new.a;
+COMMIT;
+BEGIN;
+SHOW transaction_read_only;
+ transaction_read_only
+-----------------------
+ on
+(1 row)
+
+INSERT INTO writetest VALUES (1); -- ok
+ a
+---
+ 1
+(1 row)
+
+COMMIT;
START TRANSACTION READ WRITE;
DROP TABLE writetest; -- ok
COMMIT;
diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index c670ae1..12a03fa 100644
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -51,6 +51,15 @@ EXECUTE test; -- fail
SELECT * FROM writetest, temptest; -- ok
CREATE TABLE test AS SELECT * FROM writetest; -- fail
+BEGIN;
+SET transaction_read_only = false;
+CREATE RULE write2read_rule AS ON INSERT TO writetest DO INSTEAD SELECT new.a;
+COMMIT;
+BEGIN;
+SHOW transaction_read_only;
+INSERT INTO writetest VALUES (1); -- ok
+COMMIT;
+
START TRANSACTION READ WRITE;
DROP TABLE writetest; -- ok
COMMIT;
--
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