From 16828d5c0273b4fe5f10f42588005f16b415b2d8 Mon Sep 17 00:00:00 2001 From: Andrew Dunstan Date: Wed, 28 Mar 2018 10:43:52 +1030 Subject: Fast ALTER TABLE ADD COLUMN with a non-NULL default Currently adding a column to a table with a non-NULL default results in a rewrite of the table. For large tables this can be both expensive and disruptive. This patch removes the need for the rewrite as long as the default value is not volatile. The default expression is evaluated at the time of the ALTER TABLE and the result stored in a new column (attmissingval) in pg_attribute, and a new column (atthasmissing) is set to true. Any existing row when fetched will be supplied with the attmissingval. New rows will have the supplied value or the default and so will never need the attmissingval. Any time the table is rewritten all the atthasmissing and attmissingval settings for the attributes are cleared, as they are no longer needed. The most visible code change from this is in heap_attisnull, which acquires a third TupleDesc argument, allowing it to detect a missing value if there is one. In many cases where it is known that there will not be any (e.g. catalog relations) NULL can be passed for this argument. Andrew Dunstan, heavily modified from an original patch from Serge Rielau. Reviewed by Tom Lane, Andres Freund, Tomas Vondra and David Rowley. Discussion: https://postgr.es/m/31e2e921-7002-4c27-59f5-51f08404c858@2ndQuadrant.com --- src/backend/executor/execExprInterp.c | 2 +- src/backend/executor/execMain.c | 13 +++++++++++-- src/backend/executor/execTuples.c | 28 ++++++++++++++++++++++++++-- src/backend/executor/execUtils.c | 2 ++ 4 files changed, 40 insertions(+), 5 deletions(-) (limited to 'src/backend/executor') diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c index f7bcf6370b5..e530b262dae 100644 --- a/src/backend/executor/execExprInterp.c +++ b/src/backend/executor/execExprInterp.c @@ -2505,7 +2505,7 @@ ExecEvalRowNullInt(ExprState *state, ExprEvalStep *op, /* ignore dropped columns */ if (TupleDescAttr(tupDesc, att - 1)->attisdropped) continue; - if (heap_attisnull(&tmptup, att)) + if (heap_attisnull(&tmptup, att, tupDesc)) { /* null field disproves IS NOT NULL */ if (!checkisnull) diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c index 68f6450ee64..9a107aba561 100644 --- a/src/backend/executor/execMain.c +++ b/src/backend/executor/execMain.c @@ -2980,8 +2980,17 @@ EvalPlanQualFetchRowMarks(EPQState *epqstate) false, NULL)) elog(ERROR, "failed to fetch tuple for EvalPlanQual recheck"); - /* successful, copy tuple */ - copyTuple = heap_copytuple(&tuple); + if (HeapTupleHeaderGetNatts(tuple.t_data) < + RelationGetDescr(erm->relation)->natts) + { + copyTuple = heap_expand_tuple(&tuple, + RelationGetDescr(erm->relation)); + } + else + { + /* successful, copy tuple */ + copyTuple = heap_copytuple(&tuple); + } ReleaseBuffer(buffer); } diff --git a/src/backend/executor/execTuples.c b/src/backend/executor/execTuples.c index acd1b97b0e6..78cfcadea03 100644 --- a/src/backend/executor/execTuples.c +++ b/src/backend/executor/execTuples.c @@ -625,7 +625,15 @@ ExecCopySlotMinimalTuple(TupleTableSlot *slot) if (slot->tts_mintuple) return heap_copy_minimal_tuple(slot->tts_mintuple); if (slot->tts_tuple) - return minimal_tuple_from_heap_tuple(slot->tts_tuple); + { + if (TTS_HAS_PHYSICAL_TUPLE(slot) && + HeapTupleHeaderGetNatts(slot->tts_tuple->t_data) + < slot->tts_tupleDescriptor->natts) + return minimal_expand_tuple(slot->tts_tuple, + slot->tts_tupleDescriptor); + else + return minimal_tuple_from_heap_tuple(slot->tts_tuple); + } /* * Otherwise we need to build a tuple from the Datum array. @@ -663,7 +671,23 @@ ExecFetchSlotTuple(TupleTableSlot *slot) * If we have a regular physical tuple then just return it. */ if (TTS_HAS_PHYSICAL_TUPLE(slot)) - return slot->tts_tuple; + { + if (HeapTupleHeaderGetNatts(slot->tts_tuple->t_data) < + slot->tts_tupleDescriptor->natts) + { + MemoryContext oldContext = MemoryContextSwitchTo(slot->tts_mcxt); + + slot->tts_tuple = heap_expand_tuple(slot->tts_tuple, + slot->tts_tupleDescriptor); + slot->tts_shouldFree = true; + MemoryContextSwitchTo(oldContext); + return slot->tts_tuple; + } + else + { + return slot->tts_tuple; + } + } /* * Otherwise materialize the slot... diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c index 14b07b5d449..b963cae730c 100644 --- a/src/backend/executor/execUtils.c +++ b/src/backend/executor/execUtils.c @@ -511,6 +511,8 @@ tlist_matches_tupdesc(PlanState *ps, List *tlist, Index varno, TupleDesc tupdesc return false; /* out of order */ if (att_tup->attisdropped) return false; /* table contains dropped columns */ + if (att_tup->atthasmissing) + return false; /* table contains cols with missing values */ /* * Note: usually the Var's type should match the tupdesc exactly, but -- cgit v1.2.3