Re: Remembering bug #6123
| От | Tom Lane |
|---|---|
| Тема | Re: Remembering bug #6123 |
| Дата | |
| Msg-id | 9698.1327266271@sss.pgh.pa.us обсуждение исходный текст |
| Ответ на | Re: Remembering bug #6123 ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>) |
| Ответы |
Re: Remembering bug #6123
("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
|
| Список | pgsql-hackers |
OK, here's an updated version of the patch. I changed the error message
texts as per discussion (except I decided to use one message string for
all the cases rather than saddle translators with several variants).
Also, I put in an error in GetTupleForTrigger, which fixes the
self-reference case I illustrated before (now added to the regression
test). However, I found out that changing the other two callers of
heap_lock_tuple would open an entirely new can of worms, so for now
they still have the historical behavior of ignoring self-updated tuples.
The problem with changing ExecLockRows or EvalPlanQualFetch can be
illustrated by the regression test case it breaks, which basically is
BEGIN;
DECLARE c1 CURSOR FOR SELECT * FROM table FOR UPDATE;
UPDATE table SET ...;
FETCH ALL FROM c1;
COMMIT;
When the FETCH comes to a row that's been updated by the UPDATE, it sees
that row as HeapTupleSelfUpdated with a cmax greater than es_output_cid
(which is the CID assigned to the DECLARE). So if we make these callers
throw an error for the case, coding like the above will fail, which
seems to me to be pretty darn hard to justify. It is not a corner case
that could be caused only by questionable use of trigger side effects.
So that seems to leave us with two choices: (1) ignore the row, or
(2) attempt to lock the latest version instead of the visible version.
(1) is our historical behavior but seems arguably wrong. I tried to
make the patch do (2) but it crashed and burned because heap_lock_tuple
spits up if asked to lock an "invisible" row. We could possibly finesse
that by having EvalPlanQualFetch sometimes pass a CID later than
es_output_cid to heap_lock_tuple, but it seems ticklish. More, I think
it would also take some adjustments to the behavior of
HeapTupleSatisfiesDirty, else we'll not see such tuples in the first
place. So this looks messy, and also rather orthogonal to the current
goals of the patch.
Also, I'm not sure that your testing would exercise such cases at all,
as you have to be using SELECT FOR UPDATE and/or READ COMMITTED mode to
get to any of the relevant code. I gather your software mostly relies
on SERIALIZABLE mode to avoid such issues. So I stopped with this.
regards, tom lane
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 99a431a95ff0662c82de5dfbd253f00777ca2c7c..25cbbd3ef283022d4fa7634dc79537efe9dfb735 100644
*** a/src/backend/access/heap/heapam.c
--- b/src/backend/access/heap/heapam.c
*************** simple_heap_insert(Relation relation, He
*** 2317,2343 ****
*
* relation - table to be modified (caller must hold suitable lock)
* tid - TID of tuple to be deleted
- * ctid - output parameter, used only for failure case (see below)
- * update_xmax - output parameter, used only for failure case (see below)
* cid - delete command ID (used for visibility test, and stored into
* cmax if successful)
* crosscheck - if not InvalidSnapshot, also check tuple against this
* wait - true if should wait for any conflicting update to commit/abort
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
* actually means we did delete it. Failure return codes are
* HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
* (the last only possible if wait == false).
*
! * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
! * If t_ctid is the same as tid, the tuple was deleted; if different, the
! * tuple was updated, and t_ctid is the location of the replacement tuple.
! * (t_xmax is needed to verify that the replacement tuple matches.)
*/
HTSU_Result
heap_delete(Relation relation, ItemPointer tid,
! ItemPointer ctid, TransactionId *update_xmax,
! CommandId cid, Snapshot crosscheck, bool wait)
{
HTSU_Result result;
TransactionId xid = GetCurrentTransactionId();
--- 2317,2342 ----
*
* relation - table to be modified (caller must hold suitable lock)
* tid - TID of tuple to be deleted
* cid - delete command ID (used for visibility test, and stored into
* cmax if successful)
* crosscheck - if not InvalidSnapshot, also check tuple against this
* wait - true if should wait for any conflicting update to commit/abort
+ * hufd - output parameter, filled in failure cases (see below)
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
* actually means we did delete it. Failure return codes are
* HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
* (the last only possible if wait == false).
*
! * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
! * t_xmax, and t_cmax (the last only for HeapTupleSelfUpdated, since we
! * cannot obtain cmax from a combocid generated by another transaction).
! * See comments for struct HeapUpdateFailureData for additional info.
*/
HTSU_Result
heap_delete(Relation relation, ItemPointer tid,
! CommandId cid, Snapshot crosscheck, bool wait,
! HeapUpdateFailureData *hufd)
{
HTSU_Result result;
TransactionId xid = GetCurrentTransactionId();
*************** l1:
*** 2498,2505 ****
result == HeapTupleUpdated ||
result == HeapTupleBeingUpdated);
Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
! *ctid = tp.t_data->t_ctid;
! *update_xmax = HeapTupleHeaderGetXmax(tp.t_data);
UnlockReleaseBuffer(buffer);
if (have_tuple_lock)
UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
--- 2497,2508 ----
result == HeapTupleUpdated ||
result == HeapTupleBeingUpdated);
Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
! hufd->ctid = tp.t_data->t_ctid;
! hufd->xmax = HeapTupleHeaderGetXmax(tp.t_data);
! if (result == HeapTupleSelfUpdated)
! hufd->cmax = HeapTupleHeaderGetCmax(tp.t_data);
! else
! hufd->cmax = 0; /* for lack of an InvalidCommandId value */
UnlockReleaseBuffer(buffer);
if (have_tuple_lock)
UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
*************** void
*** 2631,2643 ****
simple_heap_delete(Relation relation, ItemPointer tid)
{
HTSU_Result result;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
result = heap_delete(relation, tid,
- &update_ctid, &update_xmax,
GetCurrentCommandId(true), InvalidSnapshot,
! true /* wait for commit */ );
switch (result)
{
case HeapTupleSelfUpdated:
--- 2634,2645 ----
simple_heap_delete(Relation relation, ItemPointer tid)
{
HTSU_Result result;
! HeapUpdateFailureData hufd;
result = heap_delete(relation, tid,
GetCurrentCommandId(true), InvalidSnapshot,
! true /* wait for commit */,
! &hufd);
switch (result)
{
case HeapTupleSelfUpdated:
*************** simple_heap_delete(Relation relation, It
*** 2668,2679 ****
* relation - table to be modified (caller must hold suitable lock)
* otid - TID of old tuple to be replaced
* newtup - newly constructed tuple data to store
- * ctid - output parameter, used only for failure case (see below)
- * update_xmax - output parameter, used only for failure case (see below)
* cid - update command ID (used for visibility test, and stored into
* cmax/cmin if successful)
* crosscheck - if not InvalidSnapshot, also check old tuple against this
* wait - true if should wait for any conflicting update to commit/abort
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
* actually means we *did* update it. Failure return codes are
--- 2670,2680 ----
* relation - table to be modified (caller must hold suitable lock)
* otid - TID of old tuple to be replaced
* newtup - newly constructed tuple data to store
* cid - update command ID (used for visibility test, and stored into
* cmax/cmin if successful)
* crosscheck - if not InvalidSnapshot, also check old tuple against this
* wait - true if should wait for any conflicting update to commit/abort
+ * hufd - output parameter, filled in failure cases (see below)
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
* actually means we *did* update it. Failure return codes are
*************** simple_heap_delete(Relation relation, It
*** 2686,2700 ****
* update was done. However, any TOAST changes in the new tuple's
* data are not reflected into *newtup.
*
! * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
! * If t_ctid is the same as otid, the tuple was deleted; if different, the
! * tuple was updated, and t_ctid is the location of the replacement tuple.
! * (t_xmax is needed to verify that the replacement tuple matches.)
*/
HTSU_Result
heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
! ItemPointer ctid, TransactionId *update_xmax,
! CommandId cid, Snapshot crosscheck, bool wait)
{
HTSU_Result result;
TransactionId xid = GetCurrentTransactionId();
--- 2687,2701 ----
* update was done. However, any TOAST changes in the new tuple's
* data are not reflected into *newtup.
*
! * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
! * t_xmax, and t_cmax (the last only for HeapTupleSelfUpdated, since we
! * cannot obtain cmax from a combocid generated by another transaction).
! * See comments for struct HeapUpdateFailureData for additional info.
*/
HTSU_Result
heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
! CommandId cid, Snapshot crosscheck, bool wait,
! HeapUpdateFailureData *hufd)
{
HTSU_Result result;
TransactionId xid = GetCurrentTransactionId();
*************** l2:
*** 2873,2880 ****
result == HeapTupleUpdated ||
result == HeapTupleBeingUpdated);
Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
! *ctid = oldtup.t_data->t_ctid;
! *update_xmax = HeapTupleHeaderGetXmax(oldtup.t_data);
UnlockReleaseBuffer(buffer);
if (have_tuple_lock)
UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
--- 2874,2885 ----
result == HeapTupleUpdated ||
result == HeapTupleBeingUpdated);
Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
! hufd->ctid = oldtup.t_data->t_ctid;
! hufd->xmax = HeapTupleHeaderGetXmax(oldtup.t_data);
! if (result == HeapTupleSelfUpdated)
! hufd->cmax = HeapTupleHeaderGetCmax(oldtup.t_data);
! else
! hufd->cmax = 0; /* for lack of an InvalidCommandId value */
UnlockReleaseBuffer(buffer);
if (have_tuple_lock)
UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
*************** void
*** 3344,3356 ****
simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
{
HTSU_Result result;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
result = heap_update(relation, otid, tup,
- &update_ctid, &update_xmax,
GetCurrentCommandId(true), InvalidSnapshot,
! true /* wait for commit */ );
switch (result)
{
case HeapTupleSelfUpdated:
--- 3349,3360 ----
simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
{
HTSU_Result result;
! HeapUpdateFailureData hufd;
result = heap_update(relation, otid, tup,
GetCurrentCommandId(true), InvalidSnapshot,
! true /* wait for commit */,
! &hufd);
switch (result)
{
case HeapTupleSelfUpdated:
*************** simple_heap_update(Relation relation, It
*** 3388,3405 ****
* Output parameters:
* *tuple: all fields filled in
* *buffer: set to buffer holding tuple (pinned but not locked at exit)
! * *ctid: set to tuple's t_ctid, but only in failure cases
! * *update_xmax: set to tuple's xmax, but only in failure cases
*
* Function result may be:
* HeapTupleMayBeUpdated: lock was successfully acquired
* HeapTupleSelfUpdated: lock failed because tuple updated by self
* HeapTupleUpdated: lock failed because tuple updated by other xact
*
! * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
! * If t_ctid is the same as t_self, the tuple was deleted; if different, the
! * tuple was updated, and t_ctid is the location of the replacement tuple.
! * (t_xmax is needed to verify that the replacement tuple matches.)
*
*
* NOTES: because the shared-memory lock table is of finite size, but users
--- 3392,3408 ----
* Output parameters:
* *tuple: all fields filled in
* *buffer: set to buffer holding tuple (pinned but not locked at exit)
! * *hufd: filled in failure cases (see below)
*
* Function result may be:
* HeapTupleMayBeUpdated: lock was successfully acquired
* HeapTupleSelfUpdated: lock failed because tuple updated by self
* HeapTupleUpdated: lock failed because tuple updated by other xact
*
! * In the failure cases, the routine fills *hufd with the tuple's t_ctid,
! * t_xmax, and t_cmax (the last only for HeapTupleSelfUpdated, since we
! * cannot obtain cmax from a combocid generated by another transaction).
! * See comments for struct HeapUpdateFailureData for additional info.
*
*
* NOTES: because the shared-memory lock table is of finite size, but users
*************** simple_heap_update(Relation relation, It
*** 3435,3443 ****
* conflict for a tuple, we don't incur any extra overhead.
*/
HTSU_Result
! heap_lock_tuple(Relation relation, HeapTuple tuple, Buffer *buffer,
! ItemPointer ctid, TransactionId *update_xmax,
! CommandId cid, LockTupleMode mode, bool nowait)
{
HTSU_Result result;
ItemPointer tid = &(tuple->t_self);
--- 3438,3446 ----
* conflict for a tuple, we don't incur any extra overhead.
*/
HTSU_Result
! heap_lock_tuple(Relation relation, HeapTuple tuple,
! CommandId cid, LockTupleMode mode, bool nowait,
! Buffer *buffer, HeapUpdateFailureData *hufd)
{
HTSU_Result result;
ItemPointer tid = &(tuple->t_self);
*************** l3:
*** 3622,3629 ****
{
Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
! *ctid = tuple->t_data->t_ctid;
! *update_xmax = HeapTupleHeaderGetXmax(tuple->t_data);
LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
if (have_tuple_lock)
UnlockTuple(relation, tid, tuple_lock_type);
--- 3625,3636 ----
{
Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
! hufd->ctid = tuple->t_data->t_ctid;
! hufd->xmax = HeapTupleHeaderGetXmax(tuple->t_data);
! if (result == HeapTupleSelfUpdated)
! hufd->cmax = HeapTupleHeaderGetCmax(tuple->t_data);
! else
! hufd->cmax = 0; /* for lack of an InvalidCommandId value */
LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
if (have_tuple_lock)
UnlockTuple(relation, tid, tuple_lock_type);
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index f5e12e5681ddfbcc041bf636140d5179d0e45152..f349bedae7721a47dd47cfedb824152a6208c2b9 100644
*** a/src/backend/commands/trigger.c
--- b/src/backend/commands/trigger.c
*************** GetTupleForTrigger(EState *estate,
*** 2565,2572 ****
if (newSlot != NULL)
{
HTSU_Result test;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
*newSlot = NULL;
--- 2565,2571 ----
if (newSlot != NULL)
{
HTSU_Result test;
! HeapUpdateFailureData hufd;
*newSlot = NULL;
*************** GetTupleForTrigger(EState *estate,
*** 2578,2590 ****
*/
ltrmark:;
tuple.t_self = *tid;
! test = heap_lock_tuple(relation, &tuple, &buffer,
! &update_ctid, &update_xmax,
estate->es_output_cid,
! LockTupleExclusive, false);
switch (test)
{
case HeapTupleSelfUpdated:
/* treat it as deleted; do not process */
ReleaseBuffer(buffer);
return NULL;
--- 2577,2603 ----
*/
ltrmark:;
tuple.t_self = *tid;
! test = heap_lock_tuple(relation, &tuple,
estate->es_output_cid,
! LockTupleExclusive, false /* wait */,
! &buffer, &hufd);
switch (test)
{
case HeapTupleSelfUpdated:
+ /*
+ * The target tuple was already updated or deleted by the
+ * current command, or by a later command in the current
+ * transaction. We ignore the tuple in the former case, and
+ * throw error in the latter case, for the same reasons
+ * enumerated in ExecUpdate and ExecDelete in
+ * nodeModifyTable.c.
+ */
+ if (hufd.cmax != estate->es_output_cid)
+ ereport(ERROR,
+ (errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
+ errmsg("tuple to be updated was already modified by an operation triggered by the
currentcommand"),
+ errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate
changesto other rows.")));
+
/* treat it as deleted; do not process */
ReleaseBuffer(buffer);
return NULL;
*************** ltrmark:;
*** 2598,2604 ****
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(&update_ctid, &tuple.t_self))
{
/* it was updated, so look at the updated version */
TupleTableSlot *epqslot;
--- 2611,2617 ----
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(&hufd.ctid, &tuple.t_self))
{
/* it was updated, so look at the updated version */
TupleTableSlot *epqslot;
*************** ltrmark:;
*** 2607,2617 ****
epqstate,
relation,
relinfo->ri_RangeTableIndex,
! &update_ctid,
! update_xmax);
if (!TupIsNull(epqslot))
{
! *tid = update_ctid;
*newSlot = epqslot;
/*
--- 2620,2630 ----
epqstate,
relation,
relinfo->ri_RangeTableIndex,
! &hufd.ctid,
! hufd.xmax);
if (!TupIsNull(epqslot))
{
! *tid = hufd.ctid;
*newSlot = epqslot;
/*
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 422f737e82dcb1202d3f9e927fe87f06f6b33c7b..f71784ccb51c9d0c58668f5d803f6dc00c1e5c92 100644
*** a/src/backend/executor/execMain.c
--- b/src/backend/executor/execMain.c
*************** EvalPlanQualFetch(EState *estate, Relati
*** 1857,1864 ****
if (heap_fetch(relation, &SnapshotDirty, &tuple, &buffer, true, NULL))
{
HTSU_Result test;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
/*
* If xmin isn't what we're expecting, the slot must have been
--- 1857,1863 ----
if (heap_fetch(relation, &SnapshotDirty, &tuple, &buffer, true, NULL))
{
HTSU_Result test;
! HeapUpdateFailureData hufd;
/*
* If xmin isn't what we're expecting, the slot must have been
*************** EvalPlanQualFetch(EState *estate, Relati
*** 1893,1905 ****
/*
* If tuple was inserted by our own transaction, we have to check
* cmin against es_output_cid: cmin >= current CID means our
! * command cannot see the tuple, so we should ignore it. Without
! * this we are open to the "Halloween problem" of indefinitely
! * re-updating the same tuple. (We need not check cmax because
! * HeapTupleSatisfiesDirty will consider a tuple deleted by our
! * transaction dead, regardless of cmax.) We just checked that
! * priorXmax == xmin, so we can test that variable instead of
! * doing HeapTupleHeaderGetXmin again.
*/
if (TransactionIdIsCurrentTransactionId(priorXmax) &&
HeapTupleHeaderGetCmin(tuple.t_data) >= estate->es_output_cid)
--- 1892,1904 ----
/*
* If tuple was inserted by our own transaction, we have to check
* cmin against es_output_cid: cmin >= current CID means our
! * command cannot see the tuple, so we should ignore it.
! * Otherwise heap_lock_tuple() will throw an error, and so would
! * any later attempt to update or delete the tuple. (We need not
! * check cmax because HeapTupleSatisfiesDirty will consider a
! * tuple deleted by our transaction dead, regardless of cmax.)
! * Wee just checked that priorXmax == xmin, so we can test that
! * variable instead of doing HeapTupleHeaderGetXmin again.
*/
if (TransactionIdIsCurrentTransactionId(priorXmax) &&
HeapTupleHeaderGetCmin(tuple.t_data) >= estate->es_output_cid)
*************** EvalPlanQualFetch(EState *estate, Relati
*** 1911,1927 ****
/*
* This is a live tuple, so now try to lock it.
*/
! test = heap_lock_tuple(relation, &tuple, &buffer,
! &update_ctid, &update_xmax,
estate->es_output_cid,
! lockmode, false);
/* We now have two pins on the buffer, get rid of one */
ReleaseBuffer(buffer);
switch (test)
{
case HeapTupleSelfUpdated:
! /* treat it as deleted; do not process */
ReleaseBuffer(buffer);
return NULL;
--- 1910,1938 ----
/*
* This is a live tuple, so now try to lock it.
*/
! test = heap_lock_tuple(relation, &tuple,
estate->es_output_cid,
! lockmode, false /* wait */,
! &buffer, &hufd);
/* We now have two pins on the buffer, get rid of one */
ReleaseBuffer(buffer);
switch (test)
{
case HeapTupleSelfUpdated:
! /*
! * The target tuple was already updated or deleted by the
! * current command, or by a later command in the current
! * transaction. We *must* ignore the tuple in the former
! * case, so as to avoid the "Halloween problem" of
! * repeated update attempts. In the latter case it might
! * be sensible to fetch the updated tuple instead, but
! * doing so would require changing heap_lock_tuple as well
! * as heap_update and heap_delete to not complain about
! * updating "invisible" tuples, which seems pretty scary.
! * So for now, treat the tuple as deleted and do not
! * process.
! */
ReleaseBuffer(buffer);
return NULL;
*************** EvalPlanQualFetch(EState *estate, Relati
*** 1935,1946 ****
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(&update_ctid, &tuple.t_self))
{
/* it was updated, so look at the updated version */
! tuple.t_self = update_ctid;
/* updated row should have xmin matching this xmax */
! priorXmax = update_xmax;
continue;
}
/* tuple was deleted, so give up */
--- 1946,1957 ----
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(&hufd.ctid, &tuple.t_self))
{
/* it was updated, so look at the updated version */
! tuple.t_self = hufd.ctid;
/* updated row should have xmin matching this xmax */
! priorXmax = hufd.xmax;
continue;
}
/* tuple was deleted, so give up */
diff --git a/src/backend/executor/nodeLockRows.c b/src/backend/executor/nodeLockRows.c
index d2a33cb35682e23168d509cffe5f5f179f25249b..04ce18b0f5737ef9a55a1d88f9fb4b58a07df9ac 100644
*** a/src/backend/executor/nodeLockRows.c
--- b/src/backend/executor/nodeLockRows.c
*************** lnext:
*** 70,77 ****
bool isNull;
HeapTupleData tuple;
Buffer buffer;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
LockTupleMode lockmode;
HTSU_Result test;
HeapTuple copyTuple;
--- 70,76 ----
bool isNull;
HeapTupleData tuple;
Buffer buffer;
! HeapUpdateFailureData hufd;
LockTupleMode lockmode;
HTSU_Result test;
HeapTuple copyTuple;
*************** lnext:
*** 116,130 ****
else
lockmode = LockTupleShared;
! test = heap_lock_tuple(erm->relation, &tuple, &buffer,
! &update_ctid, &update_xmax,
estate->es_output_cid,
! lockmode, erm->noWait);
ReleaseBuffer(buffer);
switch (test)
{
case HeapTupleSelfUpdated:
! /* treat it as deleted; do not process */
goto lnext;
case HeapTupleMayBeUpdated:
--- 115,140 ----
else
lockmode = LockTupleShared;
! test = heap_lock_tuple(erm->relation, &tuple,
estate->es_output_cid,
! lockmode, erm->noWait,
! &buffer, &hufd);
ReleaseBuffer(buffer);
switch (test)
{
case HeapTupleSelfUpdated:
! /*
! * The target tuple was already updated or deleted by the
! * current command, or by a later command in the current
! * transaction. We *must* ignore the tuple in the former
! * case, so as to avoid the "Halloween problem" of repeated
! * update attempts. In the latter case it might be sensible
! * to fetch the updated tuple instead, but doing so would
! * require changing heap_lock_tuple as well as heap_update and
! * heap_delete to not complain about updating "invisible"
! * tuples, which seems pretty scary. So for now, treat the
! * tuple as deleted and do not process.
! */
goto lnext;
case HeapTupleMayBeUpdated:
*************** lnext:
*** 136,143 ****
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (ItemPointerEquals(&update_ctid,
! &tuple.t_self))
{
/* Tuple was deleted, so don't return it */
goto lnext;
--- 146,152 ----
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (ItemPointerEquals(&hufd.ctid, &tuple.t_self))
{
/* Tuple was deleted, so don't return it */
goto lnext;
*************** lnext:
*** 145,151 ****
/* updated, so fetch and lock the updated version */
copyTuple = EvalPlanQualFetch(estate, erm->relation, lockmode,
! &update_ctid, update_xmax);
if (copyTuple == NULL)
{
--- 154,160 ----
/* updated, so fetch and lock the updated version */
copyTuple = EvalPlanQualFetch(estate, erm->relation, lockmode,
! &hufd.ctid, hufd.xmax);
if (copyTuple == NULL)
{
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 37b70b88d53f6f8589c2fbb3036e5f1dc27f95ad..cf51941f88748fbd80f7e586484ce6e82bcf592b 100644
*** a/src/backend/executor/nodeModifyTable.c
--- b/src/backend/executor/nodeModifyTable.c
*************** ExecDelete(ItemPointer tupleid,
*** 294,301 ****
ResultRelInfo *resultRelInfo;
Relation resultRelationDesc;
HTSU_Result result;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
/*
* get information on the (current) result relation
--- 294,300 ----
ResultRelInfo *resultRelInfo;
Relation resultRelationDesc;
HTSU_Result result;
! HeapUpdateFailureData hufd;
/*
* get information on the (current) result relation
*************** ExecDelete(ItemPointer tupleid,
*** 347,360 ****
*/
ldelete:;
result = heap_delete(resultRelationDesc, tupleid,
- &update_ctid, &update_xmax,
estate->es_output_cid,
estate->es_crosscheck_snapshot,
! true /* wait for commit */ );
switch (result)
{
case HeapTupleSelfUpdated:
! /* already deleted by self; nothing to do */
return NULL;
case HeapTupleMayBeUpdated:
--- 346,389 ----
*/
ldelete:;
result = heap_delete(resultRelationDesc, tupleid,
estate->es_output_cid,
estate->es_crosscheck_snapshot,
! true /* wait for commit */,
! &hufd);
switch (result)
{
case HeapTupleSelfUpdated:
! /*
! * The target tuple was already updated or deleted by the
! * current command, or by a later command in the current
! * transaction. The former case is possible in a join DELETE
! * where multiple tuples join to the same target tuple.
! * This is somewhat questionable, but Postgres has always
! * allowed it: we just ignore additional deletion attempts.
! *
! * The latter case arises if the tuple is modified by a
! * command in a BEFORE trigger, or perhaps by a command in a
! * volatile function used in the query. In such situations we
! * should not ignore the deletion, but it is equally unsafe to
! * proceed. We don't want to discard the original DELETE
! * while keeping the triggered actions based on its deletion;
! * and it would be no better to allow the original DELETE
! * while discarding updates that it triggered. The row update
! * carries some information that might be important according
! * to business rules; so throwing an error is the only safe
! * course.
! *
! * If a trigger actually intends this type of interaction,
! * it can re-execute the DELETE and then return NULL to
! * cancel the outer delete.
! */
! if (hufd.cmax != estate->es_output_cid)
! ereport(ERROR,
! (errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
! errmsg("tuple to be updated was already modified by an operation triggered by the
currentcommand"),
! errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate
changesto other rows.")));
!
! /* Else, already deleted by self; nothing to do */
return NULL;
case HeapTupleMayBeUpdated:
*************** ldelete:;
*** 365,371 ****
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(tupleid, &update_ctid))
{
TupleTableSlot *epqslot;
--- 394,400 ----
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(tupleid, &hufd.ctid))
{
TupleTableSlot *epqslot;
*************** ldelete:;
*** 373,383 ****
epqstate,
resultRelationDesc,
resultRelInfo->ri_RangeTableIndex,
! &update_ctid,
! update_xmax);
if (!TupIsNull(epqslot))
{
! *tupleid = update_ctid;
goto ldelete;
}
}
--- 402,412 ----
epqstate,
resultRelationDesc,
resultRelInfo->ri_RangeTableIndex,
! &hufd.ctid,
! hufd.xmax);
if (!TupIsNull(epqslot))
{
! *tupleid = hufd.ctid;
goto ldelete;
}
}
*************** ExecUpdate(ItemPointer tupleid,
*** 481,488 ****
ResultRelInfo *resultRelInfo;
Relation resultRelationDesc;
HTSU_Result result;
! ItemPointerData update_ctid;
! TransactionId update_xmax;
List *recheckIndexes = NIL;
/*
--- 510,516 ----
ResultRelInfo *resultRelInfo;
Relation resultRelationDesc;
HTSU_Result result;
! HeapUpdateFailureData hufd;
List *recheckIndexes = NIL;
/*
*************** lreplace:;
*** 563,576 ****
* mode transactions.
*/
result = heap_update(resultRelationDesc, tupleid, tuple,
- &update_ctid, &update_xmax,
estate->es_output_cid,
estate->es_crosscheck_snapshot,
! true /* wait for commit */ );
switch (result)
{
case HeapTupleSelfUpdated:
! /* already deleted by self; nothing to do */
return NULL;
case HeapTupleMayBeUpdated:
--- 591,633 ----
* mode transactions.
*/
result = heap_update(resultRelationDesc, tupleid, tuple,
estate->es_output_cid,
estate->es_crosscheck_snapshot,
! true /* wait for commit */,
! &hufd);
switch (result)
{
case HeapTupleSelfUpdated:
! /*
! * The target tuple was already updated or deleted by the
! * current command, or by a later command in the current
! * transaction. The former case is possible in a join UPDATE
! * where multiple tuples join to the same target tuple.
! * This is pretty questionable, but Postgres has always
! * allowed it: we just execute the first update action and
! * ignore additional update attempts.
! *
! * The latter case arises if the tuple is modified by a
! * command in a BEFORE trigger, or perhaps by a command in a
! * volatile function used in the query. In such situations we
! * should not ignore the update, but it is equally unsafe to
! * proceed. We don't want to discard the original UPDATE
! * while keeping the triggered actions based on it; and we
! * have no principled way to merge this update with the
! * previous ones. So throwing an error is the only safe
! * course.
! *
! * If a trigger actually intends this type of interaction,
! * it can re-execute the UPDATE (assuming it can figure out
! * how) and then return NULL to cancel the outer update.
! */
! if (hufd.cmax != estate->es_output_cid)
! ereport(ERROR,
! (errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
! errmsg("tuple to be updated was already modified by an operation triggered by the
currentcommand"),
! errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate
changesto other rows.")));
!
! /* Else, already updated by self; nothing to do */
return NULL;
case HeapTupleMayBeUpdated:
*************** lreplace:;
*** 581,587 ****
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(tupleid, &update_ctid))
{
TupleTableSlot *epqslot;
--- 638,644 ----
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
! if (!ItemPointerEquals(tupleid, &hufd.ctid))
{
TupleTableSlot *epqslot;
*************** lreplace:;
*** 589,599 ****
epqstate,
resultRelationDesc,
resultRelInfo->ri_RangeTableIndex,
! &update_ctid,
! update_xmax);
if (!TupIsNull(epqslot))
{
! *tupleid = update_ctid;
slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
tuple = ExecMaterializeSlot(slot);
goto lreplace;
--- 646,656 ----
epqstate,
resultRelationDesc,
resultRelInfo->ri_RangeTableIndex,
! &hufd.ctid,
! hufd.xmax);
if (!TupIsNull(epqslot))
{
! *tupleid = hufd.ctid;
slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
tuple = ExecMaterializeSlot(slot);
goto lreplace;
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index fa38803b249ffd2407d77f6efd4e0203975f2349..80d60403481c99d9fab3b4fd157f708269f43a1f 100644
*** a/src/include/access/heapam.h
--- b/src/include/access/heapam.h
*************** typedef enum
*** 35,40 ****
--- 35,63 ----
LockTupleExclusive
} LockTupleMode;
+ /*
+ * When heap_update, heap_delete, or heap_lock_tuple fail because the target
+ * tuple is already outdated, they fill in this struct to provide information
+ * to the caller about what happened.
+ * ctid is the target's ctid link: it is the same as the target's TID if the
+ * target was deleted, or the location of the replacement tuple if the target
+ * was updated.
+ * xmax is the outdating transaction's XID. If the caller wants to visit the
+ * replacement tuple, it must check that this matches before believing the
+ * replacement is really a match.
+ * cmax is the outdating command's CID, but only when the failure code is
+ * HeapTupleSelfUpdated (i.e., something in the current transaction outdated
+ * the tuple); otherwise cmax is zero. (We make this restriction because
+ * HeapTupleHeaderGetCmax doesn't work for tuples outdated in other
+ * transactions.)
+ */
+ typedef struct HeapUpdateFailureData
+ {
+ ItemPointerData ctid;
+ TransactionId xmax;
+ CommandId cmax;
+ } HeapUpdateFailureData;
+
/* ----------------
* function prototypes for heap access method
*************** extern Oid heap_insert(Relation relation
*** 100,115 ****
extern void heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
CommandId cid, int options, BulkInsertState bistate);
extern HTSU_Result heap_delete(Relation relation, ItemPointer tid,
! ItemPointer ctid, TransactionId *update_xmax,
! CommandId cid, Snapshot crosscheck, bool wait);
extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
HeapTuple newtup,
! ItemPointer ctid, TransactionId *update_xmax,
! CommandId cid, Snapshot crosscheck, bool wait);
extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
! Buffer *buffer, ItemPointer ctid,
! TransactionId *update_xmax, CommandId cid,
! LockTupleMode mode, bool nowait);
extern void heap_inplace_update(Relation relation, HeapTuple tuple);
extern bool heap_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
Buffer buf);
--- 123,137 ----
extern void heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
CommandId cid, int options, BulkInsertState bistate);
extern HTSU_Result heap_delete(Relation relation, ItemPointer tid,
! CommandId cid, Snapshot crosscheck, bool wait,
! HeapUpdateFailureData *hufd);
extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
HeapTuple newtup,
! CommandId cid, Snapshot crosscheck, bool wait,
! HeapUpdateFailureData *hufd);
extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
! CommandId cid, LockTupleMode mode, bool nowait,
! Buffer *buffer, HeapUpdateFailureData *hufd);
extern void heap_inplace_update(Relation relation, HeapTuple tuple);
extern bool heap_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
Buffer buf);
diff --git a/src/test/regress/expected/triggers.out b/src/test/regress/expected/triggers.out
index b4d391974d21e9e94e75124c1cd0e022527f68e9..2e18c9275c0984a0ac290b830b407b1080b13f01 100644
*** a/src/test/regress/expected/triggers.out
--- b/src/test/regress/expected/triggers.out
*************** NOTICE: drop cascades to 2 other object
*** 1443,1445 ****
--- 1443,1642 ----
DETAIL: drop cascades to view city_view
drop cascades to view european_city_view
DROP TABLE country_table;
+ --
+ -- Test updates to rows during firing of BEFORE ROW triggers.
+ -- As of 9.2, such cases should be rejected (see bug #6123).
+ --
+ create temp table parent (
+ aid int not null primary key,
+ val1 text,
+ val2 text,
+ val3 text,
+ val4 text,
+ bcnt int not null default 0);
+ NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "parent_pkey" for table "parent"
+ create temp table child (
+ bid int not null primary key,
+ aid int not null,
+ val1 text);
+ NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "child_pkey" for table "child"
+ create function parent_upd_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if old.val1 <> new.val1 then
+ new.val2 = new.val1;
+ delete from child where child.aid = new.aid and child.val1 = new.val1;
+ end if;
+ return new;
+ end;
+ $$;
+ create trigger parent_upd_trig before update on parent
+ for each row execute procedure parent_upd_func();
+ create function parent_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ delete from child where aid = old.aid;
+ return old;
+ end;
+ $$;
+ create trigger parent_del_trig before delete on parent
+ for each row execute procedure parent_del_func();
+ create function child_ins_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ update parent set bcnt = bcnt + 1 where aid = new.aid;
+ return new;
+ end;
+ $$;
+ create trigger child_ins_trig after insert on child
+ for each row execute procedure child_ins_func();
+ create function child_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ update parent set bcnt = bcnt - 1 where aid = old.aid;
+ return old;
+ end;
+ $$;
+ create trigger child_del_trig after delete on child
+ for each row execute procedure child_del_func();
+ insert into parent values (1, 'a', 'a', 'a', 'a', 0);
+ insert into child values (10, 1, 'b');
+ select * from parent; select * from child;
+ aid | val1 | val2 | val3 | val4 | bcnt
+ -----+------+------+------+------+------
+ 1 | a | a | a | a | 1
+ (1 row)
+
+ bid | aid | val1
+ -----+-----+------
+ 10 | 1 | b
+ (1 row)
+
+ update parent set val1 = 'b' where aid = 1; -- should fail
+ ERROR: tuple to be updated was already modified by an operation triggered by the current command
+ HINT: Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.
+ select * from parent; select * from child;
+ aid | val1 | val2 | val3 | val4 | bcnt
+ -----+------+------+------+------+------
+ 1 | a | a | a | a | 1
+ (1 row)
+
+ bid | aid | val1
+ -----+-----+------
+ 10 | 1 | b
+ (1 row)
+
+ delete from parent where aid = 1; -- should fail
+ ERROR: tuple to be updated was already modified by an operation triggered by the current command
+ HINT: Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.
+ select * from parent; select * from child;
+ aid | val1 | val2 | val3 | val4 | bcnt
+ -----+------+------+------+------+------
+ 1 | a | a | a | a | 1
+ (1 row)
+
+ bid | aid | val1
+ -----+-----+------
+ 10 | 1 | b
+ (1 row)
+
+ -- replace the trigger function with one that restarts the deletion after
+ -- having modified a child
+ create or replace function parent_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ delete from child where aid = old.aid;
+ if found then
+ delete from parent where aid = old.aid;
+ return null; -- cancel outer deletion
+ end if;
+ return old;
+ end;
+ $$;
+ delete from parent where aid = 1;
+ select * from parent; select * from child;
+ aid | val1 | val2 | val3 | val4 | bcnt
+ -----+------+------+------+------+------
+ (0 rows)
+
+ bid | aid | val1
+ -----+-----+------
+ (0 rows)
+
+ drop table parent, child;
+ drop function parent_upd_func();
+ drop function parent_del_func();
+ drop function child_ins_func();
+ drop function child_del_func();
+ -- similar case, but with a self-referencing FK so that parent and child
+ -- rows can be affected by a single operation
+ create temp table self_ref_trigger (
+ id int primary key,
+ parent int references self_ref_trigger,
+ data text,
+ nchildren int not null default 0
+ );
+ NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "self_ref_trigger_pkey" for table "self_ref_trigger"
+ create function self_ref_trigger_ins_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if new.parent is not null then
+ update self_ref_trigger set nchildren = nchildren + 1
+ where id = new.parent;
+ end if;
+ return new;
+ end;
+ $$;
+ create trigger self_ref_trigger_ins_trig before insert on self_ref_trigger
+ for each row execute procedure self_ref_trigger_ins_func();
+ create function self_ref_trigger_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if old.parent is not null then
+ update self_ref_trigger set nchildren = nchildren - 1
+ where id = old.parent;
+ end if;
+ return old;
+ end;
+ $$;
+ create trigger self_ref_trigger_del_trig before delete on self_ref_trigger
+ for each row execute procedure self_ref_trigger_del_func();
+ insert into self_ref_trigger values (1, null, 'root');
+ insert into self_ref_trigger values (2, 1, 'root child A');
+ insert into self_ref_trigger values (3, 1, 'root child B');
+ insert into self_ref_trigger values (4, 2, 'grandchild 1');
+ insert into self_ref_trigger values (5, 3, 'grandchild 2');
+ update self_ref_trigger set data = 'root!' where id = 1;
+ select * from self_ref_trigger;
+ id | parent | data | nchildren
+ ----+--------+--------------+-----------
+ 2 | 1 | root child A | 1
+ 4 | 2 | grandchild 1 | 0
+ 3 | 1 | root child B | 1
+ 5 | 3 | grandchild 2 | 0
+ 1 | | root! | 2
+ (5 rows)
+
+ delete from self_ref_trigger;
+ ERROR: tuple to be updated was already modified by an operation triggered by the current command
+ HINT: Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.
+ select * from self_ref_trigger;
+ id | parent | data | nchildren
+ ----+--------+--------------+-----------
+ 2 | 1 | root child A | 1
+ 4 | 2 | grandchild 1 | 0
+ 3 | 1 | root child B | 1
+ 5 | 3 | grandchild 2 | 0
+ 1 | | root! | 2
+ (5 rows)
+
+ drop table self_ref_trigger;
+ drop function self_ref_trigger_ins_func();
+ drop function self_ref_trigger_del_func();
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index e52131dbba2d7a45c5f9365f24721de8a07e3253..f282e800e34c4a7e1982619d8b5bfbe8a5f58794 100644
*** a/src/test/regress/sql/triggers.sql
--- b/src/test/regress/sql/triggers.sql
*************** SELECT * FROM city_view;
*** 961,963 ****
--- 961,1118 ----
DROP TABLE city_table CASCADE;
DROP TABLE country_table;
+
+ --
+ -- Test updates to rows during firing of BEFORE ROW triggers.
+ -- As of 9.2, such cases should be rejected (see bug #6123).
+ --
+
+ create temp table parent (
+ aid int not null primary key,
+ val1 text,
+ val2 text,
+ val3 text,
+ val4 text,
+ bcnt int not null default 0);
+ create temp table child (
+ bid int not null primary key,
+ aid int not null,
+ val1 text);
+
+ create function parent_upd_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if old.val1 <> new.val1 then
+ new.val2 = new.val1;
+ delete from child where child.aid = new.aid and child.val1 = new.val1;
+ end if;
+ return new;
+ end;
+ $$;
+ create trigger parent_upd_trig before update on parent
+ for each row execute procedure parent_upd_func();
+
+ create function parent_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ delete from child where aid = old.aid;
+ return old;
+ end;
+ $$;
+ create trigger parent_del_trig before delete on parent
+ for each row execute procedure parent_del_func();
+
+ create function child_ins_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ update parent set bcnt = bcnt + 1 where aid = new.aid;
+ return new;
+ end;
+ $$;
+ create trigger child_ins_trig after insert on child
+ for each row execute procedure child_ins_func();
+
+ create function child_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ update parent set bcnt = bcnt - 1 where aid = old.aid;
+ return old;
+ end;
+ $$;
+ create trigger child_del_trig after delete on child
+ for each row execute procedure child_del_func();
+
+ insert into parent values (1, 'a', 'a', 'a', 'a', 0);
+ insert into child values (10, 1, 'b');
+ select * from parent; select * from child;
+
+ update parent set val1 = 'b' where aid = 1; -- should fail
+ select * from parent; select * from child;
+
+ delete from parent where aid = 1; -- should fail
+ select * from parent; select * from child;
+
+ -- replace the trigger function with one that restarts the deletion after
+ -- having modified a child
+ create or replace function parent_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ delete from child where aid = old.aid;
+ if found then
+ delete from parent where aid = old.aid;
+ return null; -- cancel outer deletion
+ end if;
+ return old;
+ end;
+ $$;
+
+ delete from parent where aid = 1;
+ select * from parent; select * from child;
+
+ drop table parent, child;
+
+ drop function parent_upd_func();
+ drop function parent_del_func();
+ drop function child_ins_func();
+ drop function child_del_func();
+
+ -- similar case, but with a self-referencing FK so that parent and child
+ -- rows can be affected by a single operation
+
+ create temp table self_ref_trigger (
+ id int primary key,
+ parent int references self_ref_trigger,
+ data text,
+ nchildren int not null default 0
+ );
+
+ create function self_ref_trigger_ins_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if new.parent is not null then
+ update self_ref_trigger set nchildren = nchildren + 1
+ where id = new.parent;
+ end if;
+ return new;
+ end;
+ $$;
+ create trigger self_ref_trigger_ins_trig before insert on self_ref_trigger
+ for each row execute procedure self_ref_trigger_ins_func();
+
+ create function self_ref_trigger_del_func()
+ returns trigger language plpgsql as
+ $$
+ begin
+ if old.parent is not null then
+ update self_ref_trigger set nchildren = nchildren - 1
+ where id = old.parent;
+ end if;
+ return old;
+ end;
+ $$;
+ create trigger self_ref_trigger_del_trig before delete on self_ref_trigger
+ for each row execute procedure self_ref_trigger_del_func();
+
+ insert into self_ref_trigger values (1, null, 'root');
+ insert into self_ref_trigger values (2, 1, 'root child A');
+ insert into self_ref_trigger values (3, 1, 'root child B');
+ insert into self_ref_trigger values (4, 2, 'grandchild 1');
+ insert into self_ref_trigger values (5, 3, 'grandchild 2');
+
+ update self_ref_trigger set data = 'root!' where id = 1;
+
+ select * from self_ref_trigger;
+
+ delete from self_ref_trigger;
+
+ select * from self_ref_trigger;
+
+ drop table self_ref_trigger;
+ drop function self_ref_trigger_ins_func();
+ drop function self_ref_trigger_del_func();
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