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Allow committing inside cursor loop

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Previously, committing or aborting inside a cursor loop was prohibited
because that would close and remove the cursor.  To allow that,
automatically convert such cursors to holdable cursors so they survive
commits or rollbacks.  Portals now have a new state "auto-held", which
means they have been converted automatically from pinned.  An auto-held
portal is kept on transaction commit or rollback, but is still removed
when returning to the main loop on error.

This supports all languages that have cursor loop constructs: PL/pgSQL,
PL/Python, PL/Perl.

Reviewed-by: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
This commit is contained in:
Peter Eisentraut
2018-03-28 18:57:10 -04:00
parent a2894cce54
commit 056a5a3f63
15 changed files with 534 additions and 87 deletions
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71
src/pl/plperl/expected/plperl_transaction.out
View File

@@ -105,11 +105,44 @@ while (defined($row = spi_fetchrow($sth))) {
spi_commit();
}
$$;
ERROR: cannot commit transaction while a cursor is open at line 6.
CONTEXT: PL/Perl anonymous code block
SELECT * FROM test1;
a | b
---+---
0 |
1 |
2 |
3 |
4 |
(5 rows)
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plperl $$
my $sth = spi_query("SELECT * FROM test2 ORDER BY x");
my $row;
while (defined($row = spi_fetchrow($sth))) {
spi_exec_query("INSERT INTO test1 (a) VALUES (12/(" . $row->{x} . "-2))");
spi_commit();
}
$$;
ERROR: division by zero at line 5.
CONTEXT: PL/Perl anonymous code block
SELECT * FROM test1;
a | b
-----+---
-6 |
-12 |
(2 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- rollback inside cursor loop
@@ -122,12 +155,42 @@ while (defined($row = spi_fetchrow($sth))) {
spi_rollback();
}
$$;
ERROR: cannot abort transaction while a cursor is open at line 6.
CONTEXT: PL/Perl anonymous code block
SELECT * FROM test1;
a | b
---+---
(0 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plperl $$
my $sth = spi_query("SELECT * FROM test2 ORDER BY x");
my $row;
while (defined($row = spi_fetchrow($sth))) {
spi_exec_query("INSERT INTO test1 (a) VALUES (" . $row->{x} . ")");
if ($row->{x} % 2 == 0) {
spi_commit();
} else {
spi_rollback();
}
}
$$;
SELECT * FROM test1;
a | b
---+---
0 |
2 |
4 |
(3 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
DROP TABLE test1;
DROP TABLE test2;

10
src/pl/plperl/plperl.c
View File

@@ -3965,10 +3965,7 @@ plperl_spi_commit(void)
PG_TRY();
{
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot commit transaction while a cursor is open")));
HoldPinnedPortals();
SPI_commit();
SPI_start_transaction();
@@ -3995,10 +3992,7 @@ plperl_spi_rollback(void)
PG_TRY();
{
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
errmsg("cannot abort transaction while a cursor is open")));
HoldPinnedPortals();
SPI_rollback();
SPI_start_transaction();

43
src/pl/plperl/sql/plperl_transaction.sql
View File

@@ -100,6 +100,26 @@ $$;
SELECT * FROM test1;
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plperl $$
my $sth = spi_query("SELECT * FROM test2 ORDER BY x");
my $row;
while (defined($row = spi_fetchrow($sth))) {
spi_exec_query("INSERT INTO test1 (a) VALUES (12/(" . $row->{x} . "-2))");
spi_commit();
}
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- rollback inside cursor loop
TRUNCATE test1;
@@ -115,6 +135,29 @@ $$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plperl $$
my $sth = spi_query("SELECT * FROM test2 ORDER BY x");
my $row;
while (defined($row = spi_fetchrow($sth))) {
spi_exec_query("INSERT INTO test1 (a) VALUES (" . $row->{x} . ")");
if ($row->{x} % 2 == 0) {
spi_commit();
} else {
spi_rollback();
}
}
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
DROP TABLE test1;
DROP TABLE test2;

108
src/pl/plpgsql/src/expected/plpgsql_transaction.out
View File

@@ -195,11 +195,47 @@ BEGIN
END LOOP;
END;
$$;
ERROR: committing inside a cursor loop is not supported
CONTEXT: PL/pgSQL function inline_code_block line 7 at COMMIT
SELECT * FROM test1;
a | b
---+---
0 |
1 |
2 |
3 |
4 |
(5 rows)
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN SELECT * FROM test2 ORDER BY x LOOP
INSERT INTO test1 (a) VALUES (12/(r.x-2));
COMMIT;
END LOOP;
END;
$$;
ERROR: division by zero
CONTEXT: SQL statement "INSERT INTO test1 (a) VALUES (12/(r.x-2))"
PL/pgSQL function inline_code_block line 6 at SQL statement
SELECT * FROM test1;
a | b
-----+---
-6 |
-12 |
(2 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- rollback inside cursor loop
@@ -214,13 +250,79 @@ BEGIN
END LOOP;
END;
$$;
ERROR: cannot abort transaction inside a cursor loop
SELECT * FROM test1;
a | b
---+---
(0 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN SELECT * FROM test2 ORDER BY x LOOP
INSERT INTO test1 (a) VALUES (r.x);
IF r.x % 2 = 0 THEN
COMMIT;
ELSE
ROLLBACK;
END IF;
END LOOP;
END;
$$;
SELECT * FROM test1;
a | b
---+---
0 |
2 |
4 |
(3 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN UPDATE test2 SET x = x * 2 RETURNING x LOOP
INSERT INTO test1 (a) VALUES (r.x);
ROLLBACK;
END LOOP;
END;
$$;
ERROR: cannot perform transaction commands inside a cursor loop that is not read-only
CONTEXT: PL/pgSQL function inline_code_block line 7 at ROLLBACK
SELECT * FROM test1;
a | b
---+---
(0 rows)
SELECT * FROM test2;
x
---
0
1
2
3
4
(5 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- commit inside block with exception handler
TRUNCATE test1;
DO LANGUAGE plpgsql $$

18
src/pl/plpgsql/src/pl_exec.c
View File

@@ -4677,14 +4677,7 @@ exec_stmt_close(PLpgSQL_execstate *estate, PLpgSQL_stmt_close *stmt)
static int
exec_stmt_commit(PLpgSQL_execstate *estate, PLpgSQL_stmt_commit *stmt)
{
/*
* XXX This could be implemented by converting the pinned portals to
* holdable ones and organizing the cleanup separately.
*/
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("committing inside a cursor loop is not supported")));
HoldPinnedPortals();
SPI_commit();
SPI_start_transaction();
@@ -4703,14 +4696,7 @@ exec_stmt_commit(PLpgSQL_execstate *estate, PLpgSQL_stmt_commit *stmt)
static int
exec_stmt_rollback(PLpgSQL_execstate *estate, PLpgSQL_stmt_rollback *stmt)
{
/*
* Unlike the COMMIT case above, this might not make sense at all,
* especially if the query driving the cursor loop has side effects.
*/
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
errmsg("cannot abort transaction inside a cursor loop")));
HoldPinnedPortals();
SPI_rollback();
SPI_start_transaction();

67
src/pl/plpgsql/src/sql/plpgsql_transaction.sql
View File

@@ -175,6 +175,28 @@ $$;
SELECT * FROM test1;
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN SELECT * FROM test2 ORDER BY x LOOP
INSERT INTO test1 (a) VALUES (12/(r.x-2));
COMMIT;
END LOOP;
END;
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- rollback inside cursor loop
TRUNCATE test1;
@@ -192,6 +214,51 @@ $$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN SELECT * FROM test2 ORDER BY x LOOP
INSERT INTO test1 (a) VALUES (r.x);
IF r.x % 2 = 0 THEN
COMMIT;
ELSE
ROLLBACK;
END IF;
END LOOP;
END;
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpgsql $$
DECLARE
r RECORD;
BEGIN
FOR r IN UPDATE test2 SET x = x * 2 RETURNING x LOOP
INSERT INTO test1 (a) VALUES (r.x);
ROLLBACK;
END LOOP;
END;
$$;
SELECT * FROM test1;
SELECT * FROM test2;
SELECT * FROM pg_cursors;
-- commit inside block with exception handler
TRUNCATE test1;

67
src/pl/plpython/expected/plpython_transaction.out
View File

@@ -111,11 +111,44 @@ for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (%s)" % row['x'])
plpy.commit()
$$;
ERROR: cannot commit transaction while a cursor is open
CONTEXT: PL/Python anonymous code block
SELECT * FROM test1;
a | b
---+---
0 |
1 |
2 |
3 |
4 |
(5 rows)
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plpythonu $$
for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (12/(%s-2))" % row['x'])
plpy.commit()
$$;
ERROR: spiexceptions.DivisionByZero: division by zero
CONTEXT: Traceback (most recent call last):
PL/Python anonymous code block, line 3, in <module>
plpy.execute("INSERT INTO test1 (a) VALUES (12/(%s-2))" % row['x'])
PL/Python anonymous code block
SELECT * FROM test1;
a | b
-----+---
-6 |
-12 |
(2 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- rollback inside cursor loop
@@ -125,12 +158,38 @@ for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (%s)" % row['x'])
plpy.rollback()
$$;
ERROR: cannot abort transaction while a cursor is open
CONTEXT: PL/Python anonymous code block
SELECT * FROM test1;
a | b
---+---
(0 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpythonu $$
for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (%s)" % row['x'])
if row['x'] % 2 == 0:
plpy.commit()
else:
plpy.rollback()
$$;
SELECT * FROM test1;
a | b
---+---
0 |
2 |
4 |
(3 rows)
SELECT * FROM pg_cursors;
name | statement | is_holdable | is_binary | is_scrollable | creation_time
------+-----------+-------------+-----------+---------------+---------------
(0 rows)
DROP TABLE test1;
DROP TABLE test2;

10
src/pl/plpython/plpy_plpymodule.c
View File

@@ -594,10 +594,7 @@ PLy_commit(PyObject *self, PyObject *args)
{
PLyExecutionContext *exec_ctx = PLy_current_execution_context();
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot commit transaction while a cursor is open")));
HoldPinnedPortals();
SPI_commit();
SPI_start_transaction();
@@ -613,10 +610,7 @@ PLy_rollback(PyObject *self, PyObject *args)
{
PLyExecutionContext *exec_ctx = PLy_current_execution_context();
if (ThereArePinnedPortals())
ereport(ERROR,
(errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
errmsg("cannot abort transaction while a cursor is open")));
HoldPinnedPortals();
SPI_rollback();
SPI_start_transaction();

36
src/pl/plpython/sql/plpython_transaction.sql
View File

@@ -99,6 +99,23 @@ $$;
SELECT * FROM test1;
-- check that this doesn't leak a holdable portal
SELECT * FROM pg_cursors;
-- error in cursor loop with commit
TRUNCATE test1;
DO LANGUAGE plpythonu $$
for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (12/(%s-2))" % row['x'])
plpy.commit()
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- rollback inside cursor loop
TRUNCATE test1;
@@ -111,6 +128,25 @@ $$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
-- first commit then rollback inside cursor loop
TRUNCATE test1;
DO LANGUAGE plpythonu $$
for row in plpy.cursor("SELECT * FROM test2 ORDER BY x"):
plpy.execute("INSERT INTO test1 (a) VALUES (%s)" % row['x'])
if row['x'] % 2 == 0:
plpy.commit()
else:
plpy.rollback()
$$;
SELECT * FROM test1;
SELECT * FROM pg_cursors;
DROP TABLE test1;
DROP TABLE test2;