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Commit8c43980

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Fix failure to detoast fields in composite elements of structured types.
If we have an array of records stored on disk, the individual record fieldscannot contain out-of-line TOAST pointers: the tuptoaster.c mechanisms areonly prepared to deal with TOAST pointers appearing in top-level fields ofa stored row. The same applies for ranges over composite types, nestedcomposites, etc. However, the existing code only took care of expandingsub-field TOAST pointers for the case of nested composites, not for otherstructured types containing composites. For example, given a command suchasUPDATE tab SET arraycol = ARRAY[(ROW(x,42)::mycompositetype] ...where x is a direct reference to a field of an on-disk tuple, if that fieldis long enough to be toasted out-of-line then the TOAST pointer would beinserted as-is into the array column. If the source record for x is laterdeleted, the array field value would become a dangling pointer, leadingto errors along the line of "missing chunk number 0 for toast value ..."when the value is referenced. A reproducible test case for this wasprovided by Jan Pecek, but it seems likely that some of the "missing chunknumber" reports we've heard in the past were caused by similar issues.Code-wise, the problem is that PG_DETOAST_DATUM() is not adequate toproduce a self-contained Datum value if the Datum is of composite type.Seen in this light, the problem is not just confined to arrays and ranges,but could also affect some other places where detoasting is done in thatway, for example form_index_tuple().I tried teaching the array code to apply toast_flatten_tuple_attribute()along with PG_DETOAST_DATUM() when the array element type is composite,but this was messy and imposed extra cache lookup costs whether or not anyTOAST pointers were present, indeed sometimes when the array element typeisn't even composite (since sometimes it takes a typcache lookup to findthat out). The idea of extending that approach to all the places thatcurrently use PG_DETOAST_DATUM() wasn't attractive at all.This patch instead solves the problem by decreeing that composite Datumvalues must not contain any out-of-line TOAST pointers in the first place;that is, we expand out-of-line fields at the point of constructing acomposite Datum, not at the point where we're about to insert it into alarger tuple. This rule is applied only to true composite Datums, notto tuples that are being passed around the system as tuples, so it's notas invasive as it might sound at first. With this approach, the amountof code that has to be touched for a full solution is greatly reduced,and added cache lookup costs are avoided except when there actually isa TOAST pointer that needs to be inlined.The main drawback of this approach is that we might sometimes dereferencea TOAST pointer that will never actually be used by the query, imposing arather large cost that wasn't there before. On the other side of the coin,if the field value is used multiple times then we'll come out ahead byavoiding repeat detoastings. Experimentation suggests that common SQLcoding patterns are unaffected either way, though. Applications that arevery negatively affected could be advised to modify their code to not fetchcolumns they won't be using.In future, we might consider reverting this solution in favor of detoastingonly at the point where data is about to be stored to disk, using somemethod that can drill down into multiple levels of nested structured types.That will require defining new APIs for structured types, though, so itdoesn't seem feasible as a back-patchable fix.Note that this patch changes HeapTupleGetDatum() from a macro to a functioncall; this means that any third-party code using that macro will not getprotection against creating TOAST-pointer-containing Datums until it'srecompiled. The same applies to any uses of PG_RETURN_HEAPTUPLEHEADER().It seems likely that this is not a big problem in practice: most of thetuple-returning functions in core and contrib produce outputs that couldnot possibly be toasted anyway, and the same probably holds for third-partyextensions.This bug has existed since TOAST was invented, so back-patch to allsupported branches.
1 parent920fbc1 commit8c43980

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15 files changed

+235
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15 files changed

+235
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lines changed

‎src/backend/access/common/heaptuple.c‎

Lines changed: 43 additions & 37 deletions
Original file line numberDiff line numberDiff line change
@@ -617,6 +617,41 @@ heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
617617
memcpy((char*)dest->t_data, (char*)src->t_data,src->t_len);
618618
}
619619

620+
/* ----------------
621+
*heap_copy_tuple_as_datum
622+
*
623+
*copy a tuple as a composite-type Datum
624+
* ----------------
625+
*/
626+
Datum
627+
heap_copy_tuple_as_datum(HeapTupletuple,TupleDesctupleDesc)
628+
{
629+
HeapTupleHeadertd;
630+
631+
/*
632+
* If the tuple contains any external TOAST pointers, we have to inline
633+
* those fields to meet the conventions for composite-type Datums.
634+
*/
635+
if (HeapTupleHasExternal(tuple))
636+
returntoast_flatten_tuple_to_datum(tuple->t_data,
637+
tuple->t_len,
638+
tupleDesc);
639+
640+
/*
641+
* Fast path for easy case: just make a palloc'd copy and insert the
642+
* correct composite-Datum header fields (since those may not be set if
643+
* the given tuple came from disk, rather than from heap_form_tuple).
644+
*/
645+
td= (HeapTupleHeader)palloc(tuple->t_len);
646+
memcpy((char*)td, (char*)tuple->t_data,tuple->t_len);
647+
648+
HeapTupleHeaderSetDatumLength(td,tuple->t_len);
649+
HeapTupleHeaderSetTypeId(td,tupleDesc->tdtypeid);
650+
HeapTupleHeaderSetTypMod(td,tupleDesc->tdtypmod);
651+
652+
returnPointerGetDatum(td);
653+
}
654+
620655
/*
621656
* heap_form_tuple
622657
*construct a tuple from the given values[] and isnull[] arrays,
@@ -635,7 +670,6 @@ heap_form_tuple(TupleDesc tupleDescriptor,
635670
data_len;
636671
inthoff;
637672
boolhasnull= false;
638-
Form_pg_attribute*att=tupleDescriptor->attrs;
639673
intnumberOfAttributes=tupleDescriptor->natts;
640674
inti;
641675

@@ -646,28 +680,14 @@ heap_form_tuple(TupleDesc tupleDescriptor,
646680
numberOfAttributes,MaxTupleAttributeNumber)));
647681

648682
/*
649-
* Check for nulls and embedded tuples; expand any toasted attributes in
650-
* embedded tuples. This preserves the invariant that toasting can only
651-
* go one level deep.
652-
*
653-
* We can skip calling toast_flatten_tuple_attribute() if the attribute
654-
* couldn't possibly be of composite type. All composite datums are
655-
* varlena and have alignment 'd'; furthermore they aren't arrays. Also,
656-
* if an attribute is already toasted, it must have been sent to disk
657-
* already and so cannot contain toasted attributes.
683+
* Check for nulls
658684
*/
659685
for (i=0;i<numberOfAttributes;i++)
660686
{
661687
if (isnull[i])
662-
hasnull= true;
663-
elseif (att[i]->attlen==-1&&
664-
att[i]->attalign=='d'&&
665-
att[i]->attndims==0&&
666-
!VARATT_IS_EXTENDED(DatumGetPointer(values[i])))
667688
{
668-
values[i]=toast_flatten_tuple_attribute(values[i],
669-
att[i]->atttypid,
670-
att[i]->atttypmod);
689+
hasnull= true;
690+
break;
671691
}
672692
}
673693

@@ -697,7 +717,8 @@ heap_form_tuple(TupleDesc tupleDescriptor,
697717

698718
/*
699719
* And fill in the information. Note we fill the Datum fields even though
700-
* this tuple may never become a Datum.
720+
* this tuple may never become a Datum. This lets HeapTupleHeaderGetDatum
721+
* identify the tuple type if needed.
701722
*/
702723
tuple->t_len=len;
703724
ItemPointerSetInvalid(&(tuple->t_self));
@@ -1389,7 +1410,6 @@ heap_form_minimal_tuple(TupleDesc tupleDescriptor,
13891410
data_len;
13901411
inthoff;
13911412
boolhasnull= false;
1392-
Form_pg_attribute*att=tupleDescriptor->attrs;
13931413
intnumberOfAttributes=tupleDescriptor->natts;
13941414
inti;
13951415

@@ -1400,28 +1420,14 @@ heap_form_minimal_tuple(TupleDesc tupleDescriptor,
14001420
numberOfAttributes,MaxTupleAttributeNumber)));
14011421

14021422
/*
1403-
* Check for nulls and embedded tuples; expand any toasted attributes in
1404-
* embedded tuples. This preserves the invariant that toasting can only
1405-
* go one level deep.
1406-
*
1407-
* We can skip calling toast_flatten_tuple_attribute() if the attribute
1408-
* couldn't possibly be of composite type. All composite datums are
1409-
* varlena and have alignment 'd'; furthermore they aren't arrays. Also,
1410-
* if an attribute is already toasted, it must have been sent to disk
1411-
* already and so cannot contain toasted attributes.
1423+
* Check for nulls
14121424
*/
14131425
for (i=0;i<numberOfAttributes;i++)
14141426
{
14151427
if (isnull[i])
1416-
hasnull= true;
1417-
elseif (att[i]->attlen==-1&&
1418-
att[i]->attalign=='d'&&
1419-
att[i]->attndims==0&&
1420-
!VARATT_IS_EXTENDED(values[i]))
14211428
{
1422-
values[i]=toast_flatten_tuple_attribute(values[i],
1423-
att[i]->atttypid,
1424-
att[i]->atttypmod);
1429+
hasnull= true;
1430+
break;
14251431
}
14261432
}
14271433

‎src/backend/access/common/indextuple.c‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -158,6 +158,11 @@ index_form_tuple(TupleDesc tupleDescriptor,
158158
if (tupmask&HEAP_HASVARWIDTH)
159159
infomask |=INDEX_VAR_MASK;
160160

161+
/* Also assert we got rid of external attributes */
162+
#ifdefTOAST_INDEX_HACK
163+
Assert((tupmask&HEAP_HASEXTERNAL)==0);
164+
#endif
165+
161166
/*
162167
* Here we make sure that the size will fit in the field reserved for it
163168
* in t_info.

‎src/backend/access/heap/tuptoaster.c‎

Lines changed: 44 additions & 48 deletions
Original file line numberDiff line numberDiff line change
@@ -944,6 +944,9 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
944944
*
945945
*"Flatten" a tuple to contain no out-of-line toasted fields.
946946
*(This does not eliminate compressed or short-header datums.)
947+
*
948+
*Note: we expect the caller already checked HeapTupleHasExternal(tup),
949+
*so there is no need for a short-circuit path.
947950
* ----------
948951
*/
949952
HeapTuple
@@ -1021,59 +1024,61 @@ toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
10211024

10221025

10231026
/* ----------
1024-
* toast_flatten_tuple_attribute -
1027+
* toast_flatten_tuple_to_datum -
1028+
*
1029+
*"Flatten" a tuple containing out-of-line toasted fields into a Datum.
1030+
*The result is always palloc'd in the current memory context.
1031+
*
1032+
*We have a general rule that Datums of container types (rows, arrays,
1033+
*ranges, etc) must not contain any external TOAST pointers. Without
1034+
*this rule, we'd have to look inside each Datum when preparing a tuple
1035+
*for storage, which would be expensive and would fail to extend cleanly
1036+
*to new sorts of container types.
1037+
*
1038+
*However, we don't want to say that tuples represented as HeapTuples
1039+
*can't contain toasted fields, so instead this routine should be called
1040+
*when such a HeapTuple is being converted into a Datum.
10251041
*
1026-
*If a Datum is of composite type, "flatten" it to contain no toasted fields.
1027-
*This must be invoked on any potentially-composite field that is to be
1028-
*inserted into a tuple.Doing this preserves the invariant that toasting
1029-
*goes only one level deep in a tuple.
1042+
*While we're at it, we decompress any compressed fields too. This is not
1043+
*necessary for correctness, but reflects an expectation that compression
1044+
*will be more effective if applied to the whole tuple not individual
1045+
*fields. We are not so concerned about that that we want to deconstruct
1046+
*and reconstruct tuples just to get rid of compressed fields, however.
1047+
*So callers typically won't call this unless they see that the tuple has
1048+
*at least one external field.
10301049
*
1031-
*Note that flattening does not mean expansion of short-header varlenas,
1032-
*so in one sense toasting is allowed within composite datums.
1050+
*On the other hand, in-line short-header varlena fields are left alone.
1051+
*If we "untoasted" them here, they'd just get changed back to short-header
1052+
*format anyway within heap_fill_tuple.
10331053
* ----------
10341054
*/
10351055
Datum
1036-
toast_flatten_tuple_attribute(Datumvalue,
1037-
OidtypeId,int32typeMod)
1056+
toast_flatten_tuple_to_datum(HeapTupleHeadertup,
1057+
uint32tup_len,
1058+
TupleDesctupleDesc)
10381059
{
1039-
TupleDesctupleDesc;
1040-
HeapTupleHeaderolddata;
10411060
HeapTupleHeadernew_data;
10421061
int32new_header_len;
10431062
int32new_data_len;
10441063
int32new_tuple_len;
10451064
HeapTupleDatatmptup;
1046-
Form_pg_attribute*att;
1047-
intnumAttrs;
1065+
Form_pg_attribute*att=tupleDesc->attrs;
1066+
intnumAttrs=tupleDesc->natts;
10481067
inti;
1049-
boolneed_change= false;
10501068
boolhas_nulls= false;
10511069
Datumtoast_values[MaxTupleAttributeNumber];
10521070
booltoast_isnull[MaxTupleAttributeNumber];
10531071
booltoast_free[MaxTupleAttributeNumber];
10541072

1055-
/*
1056-
* See if it's a composite type, and get the tupdesc if so.
1057-
*/
1058-
tupleDesc=lookup_rowtype_tupdesc_noerror(typeId,typeMod, true);
1059-
if (tupleDesc==NULL)
1060-
returnvalue;/* not a composite type */
1061-
1062-
att=tupleDesc->attrs;
1063-
numAttrs=tupleDesc->natts;
1064-
1065-
/*
1066-
* Break down the tuple into fields.
1067-
*/
1068-
olddata=DatumGetHeapTupleHeader(value);
1069-
Assert(typeId==HeapTupleHeaderGetTypeId(olddata));
1070-
Assert(typeMod==HeapTupleHeaderGetTypMod(olddata));
10711073
/* Build a temporary HeapTuple control structure */
1072-
tmptup.t_len=HeapTupleHeaderGetDatumLength(olddata);
1074+
tmptup.t_len=tup_len;
10731075
ItemPointerSetInvalid(&(tmptup.t_self));
10741076
tmptup.t_tableOid=InvalidOid;
1075-
tmptup.t_data=olddata;
1077+
tmptup.t_data=tup;
10761078

1079+
/*
1080+
* Break down the tuple into fields.
1081+
*/
10771082
Assert(numAttrs <=MaxTupleAttributeNumber);
10781083
heap_deform_tuple(&tmptup,tupleDesc,toast_values,toast_isnull);
10791084

@@ -1097,20 +1102,10 @@ toast_flatten_tuple_attribute(Datum value,
10971102
new_value=heap_tuple_untoast_attr(new_value);
10981103
toast_values[i]=PointerGetDatum(new_value);
10991104
toast_free[i]= true;
1100-
need_change= true;
11011105
}
11021106
}
11031107
}
11041108

1105-
/*
1106-
* If nothing to untoast, just return the original tuple.
1107-
*/
1108-
if (!need_change)
1109-
{
1110-
ReleaseTupleDesc(tupleDesc);
1111-
returnvalue;
1112-
}
1113-
11141109
/*
11151110
* Calculate the new size of the tuple.
11161111
*
@@ -1119,7 +1114,7 @@ toast_flatten_tuple_attribute(Datum value,
11191114
new_header_len= offsetof(HeapTupleHeaderData,t_bits);
11201115
if (has_nulls)
11211116
new_header_len+=BITMAPLEN(numAttrs);
1122-
if (olddata->t_infomask&HEAP_HASOID)
1117+
if (tup->t_infomask&HEAP_HASOID)
11231118
new_header_len+=sizeof(Oid);
11241119
new_header_len=MAXALIGN(new_header_len);
11251120
new_data_len=heap_compute_data_size(tupleDesc,
@@ -1131,14 +1126,16 @@ toast_flatten_tuple_attribute(Datum value,
11311126
/*
11321127
* Copy the existing tuple header, but adjust natts and t_hoff.
11331128
*/
1134-
memcpy(new_data,olddata, offsetof(HeapTupleHeaderData,t_bits));
1129+
memcpy(new_data,tup, offsetof(HeapTupleHeaderData,t_bits));
11351130
HeapTupleHeaderSetNatts(new_data,numAttrs);
11361131
new_data->t_hoff=new_header_len;
1137-
if (olddata->t_infomask&HEAP_HASOID)
1138-
HeapTupleHeaderSetOid(new_data,HeapTupleHeaderGetOid(olddata));
1132+
if (tup->t_infomask&HEAP_HASOID)
1133+
HeapTupleHeaderSetOid(new_data,HeapTupleHeaderGetOid(tup));
11391134

1140-
/*Reset thedatum length field, too */
1135+
/*Set thecomposite-Datum header fields correctly */
11411136
HeapTupleHeaderSetDatumLength(new_data,new_tuple_len);
1137+
HeapTupleHeaderSetTypeId(new_data,tupleDesc->tdtypeid);
1138+
HeapTupleHeaderSetTypMod(new_data,tupleDesc->tdtypmod);
11421139

11431140
/* Copy over the data, and fill the null bitmap if needed */
11441141
heap_fill_tuple(tupleDesc,
@@ -1155,7 +1152,6 @@ toast_flatten_tuple_attribute(Datum value,
11551152
for (i=0;i<numAttrs;i++)
11561153
if (toast_free[i])
11571154
pfree(DatumGetPointer(toast_values[i]));
1158-
ReleaseTupleDesc(tupleDesc);
11591155

11601156
returnPointerGetDatum(new_data);
11611157
}

‎src/backend/executor/execQual.c‎

Lines changed: 9 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -894,8 +894,6 @@ ExecEvalWholeRowFast(WholeRowVarExprState *wrvstate, ExprContext *econtext,
894894
{
895895
Var*variable= (Var*)wrvstate->xprstate.expr;
896896
TupleTableSlot*slot;
897-
HeapTupletuple;
898-
TupleDesctupleDesc;
899897
HeapTupleHeaderdtuple;
900898

901899
if (isDone)
@@ -925,32 +923,20 @@ ExecEvalWholeRowFast(WholeRowVarExprState *wrvstate, ExprContext *econtext,
925923
if (wrvstate->wrv_junkFilter!=NULL)
926924
slot=ExecFilterJunk(wrvstate->wrv_junkFilter,slot);
927925

928-
tuple=ExecFetchSlotTuple(slot);
929-
tupleDesc=slot->tts_tupleDescriptor;
930-
931926
/*
932-
* We have to make a copy of the tuple so we can safely insert the Datum
933-
* overhead fields, which are not set in on-disk tuples.
927+
* Copy the slot tuple and make sure any toasted fields get detoasted.
934928
*/
935-
dtuple= (HeapTupleHeader)palloc(tuple->t_len);
936-
memcpy((char*)dtuple, (char*)tuple->t_data,tuple->t_len);
937-
938-
HeapTupleHeaderSetDatumLength(dtuple,tuple->t_len);
929+
dtuple=DatumGetHeapTupleHeader(ExecFetchSlotTupleDatum(slot));
939930

940931
/*
941-
* If the Var identifies a named composite type, label thetuple with that
942-
* type; otherwise usewhat is inthetupleDesc.
932+
* If the Var identifies a named composite type, label thedatum with that
933+
* type; otherwisewe'lluse theslot's info.
943934
*/
944935
if (variable->vartype!=RECORDOID)
945936
{
946937
HeapTupleHeaderSetTypeId(dtuple,variable->vartype);
947938
HeapTupleHeaderSetTypMod(dtuple,variable->vartypmod);
948939
}
949-
else
950-
{
951-
HeapTupleHeaderSetTypeId(dtuple,tupleDesc->tdtypeid);
952-
HeapTupleHeaderSetTypMod(dtuple,tupleDesc->tdtypmod);
953-
}
954940

955941
returnPointerGetDatum(dtuple);
956942
}
@@ -1027,13 +1013,13 @@ ExecEvalWholeRowSlow(WholeRowVarExprState *wrvstate, ExprContext *econtext,
10271013
}
10281014

10291015
/*
1030-
* We have to make a copy of the tuple so we can safely insert the Datum
1031-
* overhead fields, which are not set in on-disk tuples.
1016+
* Copy the slot tuple and make sure any toasted fields get detoasted.
10321017
*/
1033-
dtuple= (HeapTupleHeader)palloc(tuple->t_len);
1034-
memcpy((char*)dtuple, (char*)tuple->t_data,tuple->t_len);
1018+
dtuple=DatumGetHeapTupleHeader(ExecFetchSlotTupleDatum(slot));
10351019

1036-
HeapTupleHeaderSetDatumLength(dtuple,tuple->t_len);
1020+
/*
1021+
* Reset datum's type ID fields to match the Var.
1022+
*/
10371023
HeapTupleHeaderSetTypeId(dtuple,variable->vartype);
10381024
HeapTupleHeaderSetTypMod(dtuple,variable->vartypmod);
10391025

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