From 8f5ac440430ab1d4b0309a76df278caa87018beb Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 17 Mar 2018 14:59:31 -0400 Subject: [PATCH] Fix WHERE CURRENT OF when the referenced cursor uses an index-only scan. "UPDATE/DELETE WHERE CURRENT OF cursor_name" failed, with an error message like "cannot extract system attribute from virtual tuple", if the cursor was using a index-only scan for the target table. Fix it by digging the current TID out of the indexscan state. It seems likely that the same failure could occur for CustomScan plans and perhaps some FDW plan types, so that leaving this to be treated as an internal error with an obscure message isn't as good an idea as it first seemed. Hence, add a bit of heaptuple.c infrastructure to let us deliver a more on-topic message. I chose to make the message match what you get for the case where execCurrentOf can't identify the target scan node at all, "cursor "foo" is not a simply updatable scan of table "bar"". Perhaps it should be different, but we can always adjust that later. In the future, it might be nice to provide hooks that would let custom scan providers and/or FDWs deal with this in other ways; but that's not a suitable topic for a back-patchable bug fix. It's been like this all along, so back-patch to all supported branches. Yugo Nagata and Tom Lane Discussion: https://postgr.es/m/20180201013349.937dfc5f.nagata@sraoss.co.jp --- src/backend/access/common/heaptuple.c | 26 ++++++++++ src/backend/executor/execCurrent.c | 75 ++++++++++++++++++++------- src/include/executor/tuptable.h | 2 + src/test/regress/expected/portals.out | 24 +++++++++ src/test/regress/sql/portals.sql | 10 ++++ 5 files changed, 119 insertions(+), 18 deletions(-) diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c index a2f67f2332..c45a48812b 100644 --- a/src/backend/access/common/heaptuple.c +++ b/src/backend/access/common/heaptuple.c @@ -1366,6 +1366,32 @@ slot_attisnull(TupleTableSlot *slot, int attnum) return heap_attisnull(tuple, attnum); } +/* + * slot_getsysattr + * This function fetches a system attribute of the slot's current tuple. + * Unlike slot_getattr, if the slot does not contain system attributes, + * this will return false (with a NULL attribute value) instead of + * throwing an error. + */ +bool +slot_getsysattr(TupleTableSlot *slot, int attnum, + Datum *value, bool *isnull) +{ + HeapTuple tuple = slot->tts_tuple; + + Assert(attnum < 0); /* else caller error */ + if (tuple == NULL || + tuple == &(slot->tts_minhdr)) + { + /* No physical tuple, or minimal tuple, so fail */ + *value = (Datum) 0; + *isnull = true; + return false; + } + *value = heap_getsysattr(tuple, attnum, slot->tts_tupleDescriptor, isnull); + return true; +} + /* * heap_freetuple */ diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c index ce7d4ac592..f70e54fe2a 100644 --- a/src/backend/executor/execCurrent.c +++ b/src/backend/executor/execCurrent.c @@ -12,6 +12,7 @@ */ #include "postgres.h" +#include "access/relscan.h" #include "access/sysattr.h" #include "catalog/pg_type.h" #include "executor/executor.h" @@ -149,16 +150,13 @@ execCurrentOf(CurrentOfExpr *cexpr, } else { - ScanState *scanstate; - bool lisnull; - Oid tuple_tableoid PG_USED_FOR_ASSERTS_ONLY; - ItemPointer tuple_tid; - /* * Without FOR UPDATE, we dig through the cursor's plan to find the * scan node. Fail if it's not there or buried underneath * aggregation. */ + ScanState *scanstate; + scanstate = search_plan_tree(queryDesc->planstate, table_oid); if (!scanstate) ereport(ERROR, @@ -183,21 +181,62 @@ execCurrentOf(CurrentOfExpr *cexpr, if (TupIsNull(scanstate->ss_ScanTupleSlot)) return false; - /* Use slot_getattr to catch any possible mistakes */ - tuple_tableoid = - DatumGetObjectId(slot_getattr(scanstate->ss_ScanTupleSlot, - TableOidAttributeNumber, - &lisnull)); - Assert(!lisnull); - tuple_tid = (ItemPointer) - DatumGetPointer(slot_getattr(scanstate->ss_ScanTupleSlot, - SelfItemPointerAttributeNumber, - &lisnull)); - Assert(!lisnull); + /* + * Extract TID of the scan's current row. The mechanism for this is + * in principle scan-type-dependent, but for most scan types, we can + * just dig the TID out of the physical scan tuple. + */ + if (IsA(scanstate, IndexOnlyScanState)) + { + /* + * For IndexOnlyScan, the tuple stored in ss_ScanTupleSlot may be + * a virtual tuple that does not have the ctid column, so we have + * to get the TID from xs_ctup.t_self. + */ + IndexScanDesc scan = ((IndexOnlyScanState *) scanstate)->ioss_ScanDesc; - Assert(tuple_tableoid == table_oid); + *current_tid = scan->xs_ctup.t_self; + } + else + { + /* + * Default case: try to fetch TID from the scan node's current + * tuple. As an extra cross-check, verify tableoid in the current + * tuple. If the scan hasn't provided a physical tuple, we have + * to fail. + */ + Datum ldatum; + bool lisnull; + ItemPointer tuple_tid; - *current_tid = *tuple_tid; +#ifdef USE_ASSERT_CHECKING + if (!slot_getsysattr(scanstate->ss_ScanTupleSlot, + TableOidAttributeNumber, + &ldatum, + &lisnull)) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", + cursor_name, table_name))); + Assert(!lisnull); + Assert(DatumGetObjectId(ldatum) == table_oid); +#endif + + if (!slot_getsysattr(scanstate->ss_ScanTupleSlot, + SelfItemPointerAttributeNumber, + &ldatum, + &lisnull)) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", + cursor_name, table_name))); + Assert(!lisnull); + tuple_tid = (ItemPointer) DatumGetPointer(ldatum); + + *current_tid = *tuple_tid; + } + + Assert(ItemPointerIsValid(current_tid)); return true; } diff --git a/src/include/executor/tuptable.h b/src/include/executor/tuptable.h index 0642a3ada5..a5779b15ea 100644 --- a/src/include/executor/tuptable.h +++ b/src/include/executor/tuptable.h @@ -170,5 +170,7 @@ extern Datum slot_getattr(TupleTableSlot *slot, int attnum, bool *isnull); extern void slot_getallattrs(TupleTableSlot *slot); extern void slot_getsomeattrs(TupleTableSlot *slot, int attnum); extern bool slot_attisnull(TupleTableSlot *slot, int attnum); +extern bool slot_getsysattr(TupleTableSlot *slot, int attnum, + Datum *value, bool *isnull); #endif /* TUPTABLE_H */ diff --git a/src/test/regress/expected/portals.out b/src/test/regress/expected/portals.out index 1b8f7b69d1..048b2fc3e3 100644 --- a/src/test/regress/expected/portals.out +++ b/src/test/regress/expected/portals.out @@ -1245,6 +1245,30 @@ FETCH FROM c1; DELETE FROM ucview WHERE CURRENT OF c1; -- fail, views not supported ERROR: WHERE CURRENT OF on a view is not implemented +ROLLBACK; +-- Check WHERE CURRENT OF with an index-only scan +BEGIN; +EXPLAIN (costs off) +DECLARE c1 CURSOR FOR SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; + QUERY PLAN +--------------------------------------------- + Index Only Scan using onek_stringu1 on onek + Index Cond: (stringu1 = 'DZAAAA'::name) +(2 rows) + +DECLARE c1 CURSOR FOR SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; +FETCH FROM c1; + stringu1 +---------- + DZAAAA +(1 row) + +DELETE FROM onek WHERE CURRENT OF c1; +SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; + stringu1 +---------- +(0 rows) + ROLLBACK; -- Make sure snapshot management works okay, per bug report in -- 235395b90909301035v7228ce63q392931f15aa74b31@mail.gmail.com diff --git a/src/test/regress/sql/portals.sql b/src/test/regress/sql/portals.sql index a1c812e937..d1a589094e 100644 --- a/src/test/regress/sql/portals.sql +++ b/src/test/regress/sql/portals.sql @@ -462,6 +462,16 @@ FETCH FROM c1; DELETE FROM ucview WHERE CURRENT OF c1; -- fail, views not supported ROLLBACK; +-- Check WHERE CURRENT OF with an index-only scan +BEGIN; +EXPLAIN (costs off) +DECLARE c1 CURSOR FOR SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; +DECLARE c1 CURSOR FOR SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; +FETCH FROM c1; +DELETE FROM onek WHERE CURRENT OF c1; +SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; +ROLLBACK; + -- Make sure snapshot management works okay, per bug report in -- 235395b90909301035v7228ce63q392931f15aa74b31@mail.gmail.com BEGIN;