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```c++
/* ----------------------------------------------------------------
* ExecUpdate
*
* note: we can't run UPDATE queries with transactions off because UPDATEs are actually INSERTs and our
* scan will mistakenly loop forever, updating the tuple it just inserted.. This should be fixed but until it
* is, we don't want to get stuck in an infinite loop which corrupts your database..
*
* When updating a table, tupleid identifies the tuple to update and oldtuple is NULL.
*
* Returns RETURNING result if any, otherwise NULL.
* ----------------------------------------------------------------*/
static TupleTableSlot *
ExecUpdate(ModifyTableState *mtstate,
ItemPointer tupleid,
HeapTuple oldtuple,
TupleTableSlot *slot,
TupleTableSlot *planSlot,
EPQState *epqstate,
EState *estate,
bool canSetTag)
{
ResultRelInfo *resultRelInfo;
Relation resultRelationDesc;
TM_Result result;
TM_FailureData tmfd;
List *recheckIndexes = NIL;
TupleConversionMap *saved_tcs_map = NULL;
/* abort the operation if not running transactions*/
if (IsBootstrapProcessingMode())
elog(ERROR, "cannot UPDATE during bootstrap");
ExecMaterializeSlot(slot);
/* get information on the (current) result relation*/
resultRelInfo = estate->es_result_relation_info;
resultRelationDesc = resultRelInfo->ri_RelationDesc;
/* BEFORE ROW UPDATE Triggers */
if (resultRelInfo->ri_TrigDesc && resultRelInfo->ri_TrigDesc->trig_update_before_row)
{
if (!ExecBRUpdateTriggers(estate, epqstate, resultRelInfo, tupleid, oldtuple, slot))
return NULL; /* "do nothing" */
}
/* INSTEAD OF ROW UPDATE Triggers */
if (resultRelInfo->ri_TrigDesc && resultRelInfo->ri_TrigDesc->trig_update_instead_row)
{
if (!ExecIRUpdateTriggers(estate, resultRelInfo, oldtuple, slot))
return NULL; /* "do nothing" */
}
else if (resultRelInfo->ri_FdwRoutine)
{
/* Compute stored generated columns*/
if (resultRelationDesc->rd_att->constr && resultRelationDesc->rd_att->constr->has_generated_stored)
ExecComputeStoredGenerated(estate, slot, CMD_UPDATE);
/* update in foreign table: let the FDW do it*/
slot = resultRelInfo->ri_FdwRoutine->ExecForeignUpdate(estate, resultRelInfo, slot, planSlot);
if (slot == NULL) /* "do nothing" */
return NULL;
/* AFTER ROW Triggers or RETURNING expressions might reference the
* tableoid column, so (re-)initialize tts_tableOid before evaluating them. */
slot->tts_tableOid = RelationGetRelid(resultRelationDesc);
}
else
{
LockTupleMode lockmode;
bool partition_constraint_failed;
bool update_indexes;
/* Constraints might reference the tableoid column, so (re-)initialize
* tts_tableOid before evaluating them.*/
slot->tts_tableOid = RelationGetRelid(resultRelationDesc);
/* Compute stored generated columns*/
if (resultRelationDesc->rd_att->constr && resultRelationDesc->rd_att->constr->has_generated_stored)
ExecComputeStoredGenerated(estate, slot, CMD_UPDATE);
/*
* Check any RLS UPDATE WITH CHECK policies
*
* If we generate a new candidate tuple after EvalPlanQual testing, we
* must loop back here and recheck any RLS policies and constraints.
* (We don't need to redo triggers, however. If there are any BEFORE
* triggers then trigger.c will have done table_tuple_lock to lock the
* correct tuple, so there's no need to do them again.) */
lreplace:;
/* ensure slot is independent, consider e.g. EPQ */
ExecMaterializeSlot(slot);
/* If partition constraint fails, this row might get moved to another
* partition, in which case we should check the RLS CHECK policy just
* before inserting into the new partition, rather than doing it here.
* This is because a trigger on that partition might again change the
* row. So skip the WCO checks if the partition constraint fails. */
partition_constraint_failed = resultRelInfo->ri_PartitionCheck && !ExecPartitionCheck(resultRelInfo, slot, estate, false);
if (!partition_constraint_failed && resultRelInfo->ri_WithCheckOptions != NIL)
{
/* ExecWithCheckOptions() will skip any WCOs which are not of the kind we are looking for at this point. */
ExecWithCheckOptions(WCO_RLS_UPDATE_CHECK, resultRelInfo, slot, estate);
}
/* If a partition check failed, try to move the row into the right partition.*/
if (partition_constraint_failed)
{
bool tuple_deleted;
TupleTableSlot *ret_slot;
TupleTableSlot *orig_slot = slot;
TupleTableSlot *epqslot = NULL;
PartitionTupleRouting *proute = mtstate->mt_partition_tuple_routing;
int map_index;
TupleConversionMap *tupconv_map;
/* Disallow an INSERT ON CONFLICT DO UPDATE that causes the
* original row to migrate to a different partition. Maybe this
* can be implemented some day, but it seems a fringe feature with
* little redeeming value.*/
if (((ModifyTable *) mtstate->ps.plan)->onConflictAction == ONCONFLICT_UPDATE)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("invalid ON UPDATE specification"),
errdetail("The result tuple would appear in a different partition than the original tuple.")));
/* When an UPDATE is run on a leaf partition, we will not have
* partition tuple routing set up. In that case, fail with
* partition constraint violation error.*/
if (proute == NULL)
ExecPartitionCheckEmitError(resultRelInfo, slot, estate);
/* Row movement, part 1. Delete the tuple, but skip RETURNING
* processing. We want to return rows from INSERT.*/
ExecDelete(mtstate, tupleid, oldtuple, planSlot, epqstate, estate, false, false /* canSetTag */ , true /* changingPart */ , &tuple_deleted, &epqslot);
/* For some reason if DELETE didn't happen (e.g. trigger prevented
* it, or it was already deleted by self, or it was concurrently
* deleted by another transaction), then we should skip the insert
* as well; otherwise, an UPDATE could cause an increase in the
* total number of rows across all partitions, which is clearly wrong.
*
* For a normal UPDATE, the case where the tuple has been the
* subject of a concurrent UPDATE or DELETE would be handled by
* the EvalPlanQual machinery, but for an UPDATE that we've
* translated into a DELETE from this partition and an INSERT into
* some other partition, that's not available, because CTID chains
* can't span relation boundaries. We mimic the semantics to a
* limited extent by skipping the INSERT if the DELETE fails to
* find a tuple. This ensures that two concurrent attempts to
* UPDATE the same tuple at the same time can't turn one tuple
* into two, and that an UPDATE of a just-deleted tuple can't resurrect it.*/
if (!tuple_deleted)
{
/*
* epqslot will be typically NULL. But when ExecDelete()
* finds that another transaction has concurrently updated the
* same row, it re-fetches the row, skips the delete, and
* epqslot is set to the re-fetched tuple slot. In that case,
* we need to do all the checks again.
*/
if (TupIsNull(epqslot))
return NULL;
else
{
slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
goto lreplace;
}
}
/* Updates set the transition capture map only when a new subplan
* is chosen. But for inserts, it is set for each row. So after
* INSERT, we need to revert back to the map created for UPDATE;
* otherwise the next UPDATE will incorrectly use the one created
* for INSERT. So first save the one created for UPDATE. */
if (mtstate->mt_transition_capture)
saved_tcs_map = mtstate->mt_transition_capture->tcs_map;
/* resultRelInfo is one of the per-subplan resultRelInfos. So we
* should convert the tuple into root's tuple descriptor, since
* ExecInsert() starts the search from root. The tuple conversion
* map list is in the order of mtstate->resultRelInfo[], so to
* retrieve the one for this resultRel, we need to know the
* position of the resultRel in mtstate->resultRelInfo[]. */
map_index = resultRelInfo - mtstate->resultRelInfo;
Assert(map_index >= 0 && map_index < mtstate->mt_nplans);
tupconv_map = tupconv_map_for_subplan(mtstate, map_index);
if (tupconv_map != NULL)
slot = execute_attr_map_slot(tupconv_map->attrMap, slot, mtstate->mt_root_tuple_slot);
/* Prepare for tuple routing, making it look like we're inserting into the root. */
Assert(mtstate->rootResultRelInfo != NULL);
slot = ExecPrepareTupleRouting(mtstate, estate, proute, mtstate->rootResultRelInfo, slot);
ret_slot = ExecInsert(mtstate, slot, planSlot,
orig_slot, resultRelInfo,
estate, canSetTag);
/* Revert ExecPrepareTupleRouting's node change. */
estate->es_result_relation_info = resultRelInfo;
if (mtstate->mt_transition_capture)
{
mtstate->mt_transition_capture->tcs_original_insert_tuple = NULL;
mtstate->mt_transition_capture->tcs_map = saved_tcs_map;
}
return ret_slot;
}
/* Check the constraints of the tuple. We've already checked the
* partition constraint above; however, we must still ensure the tuple
* passes all other constraints, so we will call ExecConstraints() and
* have it validate all remaining checks.*/
if (resultRelationDesc->rd_att->constr)
ExecConstraints(resultRelInfo, slot, estate);
/* replace the heap tuple
*
* Note: if es_crosscheck_snapshot isn't InvalidSnapshot, we check
* that the row to be updated is visible to that snapshot, and throw a
* can't-serialize error if not. This is a special-case behavior
* needed for referential integrity updates in transaction-snapshot mode transactions. */
result = table_tuple_update(resultRelationDesc, tupleid, slot, estate->es_output_cid,
estate->es_snapshot, estate->es_crosscheck_snapshot, true /* wait for commit */ ,&tmfd, &lockmode, &update_indexes);
switch (result)
{
case TM_SelfModified:
/* 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 (tmfd.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 current command"),
errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
/* Else, already updated by self; nothing to do */
return NULL;
case TM_Ok:
break;
case TM_Updated:
{
TupleTableSlot *inputslot;
TupleTableSlot *epqslot;
if (IsolationUsesXactSnapshot())
ereport(ERROR,(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),errmsg("could not serialize access due to concurrent update")));
/* Already know that we're going to need to do EPQ, so fetch tuple directly into the right slot. */
inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,resultRelInfo->ri_RangeTableIndex);
result = table_tuple_lock(resultRelationDesc, tupleid, estate->es_snapshot,inputslot, estate->es_output_cid, lockmode, LockWaitBlock, TUPLE_LOCK_FLAG_FIND_LAST_VERSION,&tmfd);
switch (result)
{
case TM_Ok:
Assert(tmfd.traversed);
epqslot = EvalPlanQual(epqstate, resultRelationDesc, resultRelInfo->ri_RangeTableIndex, inputslot);
if (TupIsNull(epqslot))
/* Tuple not passing quals anymore, exiting... */
return NULL;
slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
goto lreplace;
case TM_Deleted:
/* tuple already deleted; nothing to do */
return NULL;
case TM_SelfModified:
/*
* This can be reached when following an update chain from a tuple updated by another session,
* reaching a tuple that was already updated in this transaction. If previously modified by
* this command, ignore the redundant update, otherwise error out.
*
* See also TM_SelfModified response to table_tuple_update() above.*/
if (tmfd.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 current command"),errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
return NULL;
default:
/* see table_tuple_lock call in ExecDelete() */
elog(ERROR, "unexpected table_tuple_lock status: %u", result);
return NULL;
}
}
break;
case TM_Deleted:
if (IsolationUsesXactSnapshot())
ereport(ERROR,(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),errmsg("could not serialize access due to concurrent delete")));
/* tuple already deleted; nothing to do */
return NULL;
default:
elog(ERROR, "unrecognized table_tuple_update status: %u",
result);
return NULL;
}
/* insert index entries for tuple if necessary */
if (resultRelInfo->ri_NumIndices > 0 && update_indexes)
recheckIndexes = ExecInsertIndexTuples(slot, estate, false, NULL, NIL);
}
if (canSetTag)
(estate->es_processed)++;
/* AFTER ROW UPDATE Triggers */
ExecARUpdateTriggers(estate, resultRelInfo, tupleid, oldtuple, slot,recheckIndexes,mtstate->operation == CMD_INSERT ?mtstate->mt_oc_transition_capture : mtstate->mt_transition_capture);
list_free(recheckIndexes);
/* Check any WITH CHECK OPTION constraints from parent views. We are
* required to do this after testing all constraints and uniqueness
* violations per the SQL spec, so we do it after actually updating the
* record in the heap and all indexes.
*
* ExecWithCheckOptions() will skip any WCOs which are not of the kind we
* are looking for at this point. */
if (resultRelInfo->ri_WithCheckOptions != NIL)
ExecWithCheckOptions(WCO_VIEW_CHECK, resultRelInfo, slot, estate);
if (resultRelInfo->ri_projectReturning) /* Process RETURNING if present */
return ExecProcessReturning(resultRelInfo->ri_projectReturning,RelationGetRelid(resultRelationDesc),slot, planSlot);
return NULL;
}
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