mirror of https://github.com/postgres/postgres
The current implementation fires an AFTER ROW trigger for each tuple that looks like it might be non-unique according to the index contents at the time of insertion. This works well as long as there aren't many conflicts, but won't scale to massive unique-key reassignments. Improving that case is a TODO item. Dean RasheedREL8_5_ALPHA1_BRANCH
Tom Lane
16 years ago
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/*-------------------------------------------------------------------------
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* |
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* constraint.c |
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* PostgreSQL CONSTRAINT support code. |
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* |
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* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* IDENTIFICATION |
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* $PostgreSQL: pgsql/src/backend/commands/constraint.c,v 1.1 2009/07/29 20:56:18 tgl Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "catalog/index.h" |
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#include "commands/trigger.h" |
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#include "executor/executor.h" |
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#include "utils/builtins.h" |
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#include "utils/tqual.h" |
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|
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/*
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* unique_key_recheck - trigger function to do a deferred uniqueness check. |
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* |
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* This is invoked as an AFTER ROW trigger for both INSERT and UPDATE, |
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* for any rows recorded as potentially violating a deferrable unique |
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* constraint. |
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* |
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* This may be an end-of-statement check, a commit-time check, or a |
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* check triggered by a SET CONSTRAINTS command. |
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*/ |
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Datum |
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unique_key_recheck(PG_FUNCTION_ARGS) |
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{ |
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TriggerData *trigdata = (TriggerData *) fcinfo->context; |
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const char *funcname = "unique_key_recheck"; |
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HeapTuple new_row; |
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ItemPointerData tmptid; |
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Relation indexRel; |
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IndexInfo *indexInfo; |
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EState *estate; |
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ExprContext *econtext; |
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TupleTableSlot *slot; |
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Datum values[INDEX_MAX_KEYS]; |
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bool isnull[INDEX_MAX_KEYS]; |
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/*
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* Make sure this is being called as an AFTER ROW trigger. Note: |
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* translatable error strings are shared with ri_triggers.c, so |
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* resist the temptation to fold the function name into them. |
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*/ |
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if (!CALLED_AS_TRIGGER(fcinfo)) |
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ereport(ERROR, |
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED), |
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errmsg("function \"%s\" was not called by trigger manager", |
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funcname))); |
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if (!TRIGGER_FIRED_AFTER(trigdata->tg_event) || |
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!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event)) |
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ereport(ERROR, |
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED), |
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errmsg("function \"%s\" must be fired AFTER ROW", |
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funcname))); |
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/*
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* Get the new data that was inserted/updated. |
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*/ |
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if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event)) |
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new_row = trigdata->tg_trigtuple; |
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else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event)) |
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new_row = trigdata->tg_newtuple; |
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else |
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{ |
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ereport(ERROR, |
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(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED), |
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errmsg("function \"%s\" must be fired for INSERT or UPDATE", |
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funcname))); |
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new_row = NULL; /* keep compiler quiet */ |
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} |
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/*
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* If the new_row is now dead (ie, inserted and then deleted within our |
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* transaction), we can skip the check. However, we have to be careful, |
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* because this trigger gets queued only in response to index insertions; |
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* which means it does not get queued for HOT updates. The row we are |
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* called for might now be dead, but have a live HOT child, in which case |
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* we still need to make the uniqueness check. Therefore we have to use |
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* heap_hot_search, not just HeapTupleSatisfiesVisibility as is done in |
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* the comparable test in RI_FKey_check. |
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* |
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* This might look like just an optimization, because the index AM will |
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* make this identical test before throwing an error. But it's actually |
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* needed for correctness, because the index AM will also throw an error |
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* if it doesn't find the index entry for the row. If the row's dead then |
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* it's possible the index entry has also been marked dead, and even |
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* removed. |
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*/ |
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tmptid = new_row->t_self; |
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if (!heap_hot_search(&tmptid, trigdata->tg_relation, SnapshotSelf, NULL)) |
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{ |
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/*
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* All rows in the HOT chain are dead, so skip the check. |
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*/ |
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return PointerGetDatum(NULL); |
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} |
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/*
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* Open the index, acquiring a RowExclusiveLock, just as if we were |
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* going to update it. (This protects against possible changes of the |
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* index schema, not against concurrent updates.) |
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*/ |
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indexRel = index_open(trigdata->tg_trigger->tgconstrindid, |
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RowExclusiveLock); |
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indexInfo = BuildIndexInfo(indexRel); |
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/*
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* The heap tuple must be put into a slot for FormIndexDatum. |
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*/ |
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slot = MakeSingleTupleTableSlot(RelationGetDescr(trigdata->tg_relation)); |
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ExecStoreTuple(new_row, slot, InvalidBuffer, false); |
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/*
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* Typically the index won't have expressions, but if it does we need |
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* an EState to evaluate them. |
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*/ |
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if (indexInfo->ii_Expressions != NIL) |
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{ |
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estate = CreateExecutorState(); |
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econtext = GetPerTupleExprContext(estate); |
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econtext->ecxt_scantuple = slot; |
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} |
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else |
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estate = NULL; |
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/*
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* Form the index values and isnull flags for the index entry that |
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* we need to check. |
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* |
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* Note: if the index uses functions that are not as immutable as they |
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* are supposed to be, this could produce an index tuple different from |
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* the original. The index AM can catch such errors by verifying that |
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* it finds a matching index entry with the tuple's TID. |
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*/ |
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FormIndexDatum(indexInfo, slot, estate, values, isnull); |
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/*
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* Now do the uniqueness check. This is not a real insert; it is a |
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* check that the index entry that has already been inserted is unique. |
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*/ |
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index_insert(indexRel, values, isnull, &(new_row->t_self), |
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trigdata->tg_relation, UNIQUE_CHECK_EXISTING); |
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/*
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* If that worked, then this index entry is unique, and we are done. |
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*/ |
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if (estate != NULL) |
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FreeExecutorState(estate); |
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ExecDropSingleTupleTableSlot(slot); |
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index_close(indexRel, RowExclusiveLock); |
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return PointerGetDatum(NULL); |
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} |
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