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Commitfb0919f

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committed
Don't assume that max offset number stays fixed on a page when we're
not holding a pin on the page. Use double instead of long to countrows in relation, so that code still works for > LONG_MAX rows in rel.
1 parent6497a7f commitfb0919f

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1 file changed

+67
-66
lines changed

1 file changed

+67
-66
lines changed

‎src/backend/commands/analyze.c

Lines changed: 67 additions & 66 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/commands/analyze.c,v 1.21 2001/06/22 19:16:21 wieck Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/commands/analyze.c,v 1.22 2001/07/05 19:33:35 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -97,8 +97,8 @@ typedef struct
9797
}ScalarMCVItem;
9898

9999

100-
#defineswapInt(a,b){int _tmp; _tmp=a; a=b; b=_tmp;}
101-
#defineswapDatum(a,b){Datum _tmp; _tmp=a; a=b; b=_tmp;}
100+
#defineswapInt(a,b)do{int _tmp; _tmp=a; a=b; b=_tmp;} while(0)
101+
#defineswapDatum(a,b)do{Datum _tmp; _tmp=a; a=b; b=_tmp;} while(0)
102102

103103

104104
staticintMESSAGE_LEVEL;
@@ -111,20 +111,18 @@ static int *datumCmpTupnoLink;
111111

112112
staticVacAttrStats*examine_attribute(Relationonerel,intattnum);
113113
staticintacquire_sample_rows(Relationonerel,HeapTuple*rows,
114-
inttargrows,long*totalrows);
114+
inttargrows,double*totalrows);
115115
staticdoublerandom_fract(void);
116116
staticdoubleinit_selection_state(intn);
117-
staticlongselect_next_random_record(longt,intn,double*stateptr);
117+
staticdoubleselect_next_random_record(doublet,intn,double*stateptr);
118118
staticintcompare_rows(constvoid*a,constvoid*b);
119119
staticintcompare_scalars(constvoid*a,constvoid*b);
120120
staticintcompare_mcvs(constvoid*a,constvoid*b);
121-
staticOffsetNumberget_page_max_offset(Relationrelation,
122-
BlockNumberblocknumber);
123121
staticvoidcompute_minimal_stats(VacAttrStats*stats,
124-
TupleDesctupDesc,longtotalrows,
122+
TupleDesctupDesc,doubletotalrows,
125123
HeapTuple*rows,intnumrows);
126124
staticvoidcompute_scalar_stats(VacAttrStats*stats,
127-
TupleDesctupDesc,longtotalrows,
125+
TupleDesctupDesc,doubletotalrows,
128126
HeapTuple*rows,intnumrows);
129127
staticvoidupdate_attstats(Oidrelid,intnatts,VacAttrStats**vacattrstats);
130128

@@ -143,7 +141,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
143141
VacAttrStats**vacattrstats;
144142
inttargrows,
145143
numrows;
146-
longtotalrows;
144+
doubletotalrows;
147145
HeapTuple*rows;
148146
HeapTupletuple;
149147

@@ -298,7 +296,7 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
298296
if (!vacstmt->vacuum)
299297
vac_update_relstats(RelationGetRelid(onerel),
300298
onerel->rd_nblocks,
301-
(double)totalrows,
299+
totalrows,
302300
RelationGetForm(onerel)->relhasindex);
303301

304302
/*
@@ -488,7 +486,7 @@ examine_attribute(Relation onerel, int attnum)
488486
*/
489487
staticint
490488
acquire_sample_rows(Relationonerel,HeapTuple*rows,inttargrows,
491-
long*totalrows)
489+
double*totalrows)
492490
{
493491
intnumrows=0;
494492
HeapScanDescscan;
@@ -499,7 +497,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
499497
OffsetNumberlastoffset;
500498
intnumest;
501499
doubletuplesperpage;
502-
longt;
500+
doublet;
503501
doublerstate;
504502

505503
Assert(targrows>1);
@@ -520,7 +518,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
520518
*/
521519
if (!HeapTupleIsValid(tuple))
522520
{
523-
*totalrows=numrows;
521+
*totalrows=(double)numrows;
524522
returnnumrows;
525523
}
526524
/*
@@ -565,20 +563,22 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
565563
}
566564
tuplesperpage= (double)numest / (double)estblock;
567565

568-
t=numrows;/* t is the # of records processed so far */
566+
t=(double)numrows;/* t is the # of records processed so far */
569567
rstate=init_selection_state(targrows);
570568
for (;;)
571569
{
572570
doubletargpos;
573571
BlockNumbertargblock;
572+
Buffertargbuffer;
573+
Pagetargpage;
574574
OffsetNumbertargoffset,
575575
maxoffset;
576576

577577
t=select_next_random_record(t,targrows,&rstate);
578578
/* Try to read the t'th record in the table */
579-
targpos=(double)t /tuplesperpage;
579+
targpos=t /tuplesperpage;
580580
targblock= (BlockNumber)targpos;
581-
targoffset= ((int) (targpos-targblock)*tuplesperpage)+
581+
targoffset= ((int) ((targpos-targblock)*tuplesperpage))+
582582
FirstOffsetNumber;
583583
/* Make sure we are past the last selected record */
584584
if (targblock <=lastblock)
@@ -595,21 +595,37 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
595595
*/
596596
if (targblock >=onerel->rd_nblocks)
597597
break;
598-
maxoffset=get_page_max_offset(onerel,targblock);
598+
/*
599+
* We must maintain a pin on the target page's buffer to ensure that
600+
* the maxoffset value stays good (else concurrent VACUUM might
601+
* delete tuples out from under us). Hence, pin the page until we
602+
* are done looking at it. We don't maintain a lock on the page,
603+
* so tuples could get added to it, but we ignore such tuples.
604+
*/
605+
targbuffer=ReadBuffer(onerel,targblock);
606+
if (!BufferIsValid(targbuffer))
607+
elog(ERROR,"acquire_sample_rows: ReadBuffer(%s,%u) failed",
608+
RelationGetRelationName(onerel),targblock);
609+
LockBuffer(targbuffer,BUFFER_LOCK_SHARE);
610+
targpage=BufferGetPage(targbuffer);
611+
maxoffset=PageGetMaxOffsetNumber(targpage);
612+
LockBuffer(targbuffer,BUFFER_LOCK_UNLOCK);
613+
599614
for (;;)
600615
{
601616
HeapTupleDatatargtuple;
602-
Buffertargbuffer;
617+
Buffertupbuffer;
603618

604619
if (targoffset>maxoffset)
605620
{
606621
/* Fell off end of this page, try next */
622+
ReleaseBuffer(targbuffer);
607623
targblock++;
608624
targoffset=FirstOffsetNumber;
609625
gotopageloop;
610626
}
611627
ItemPointerSet(&targtuple.t_self,targblock,targoffset);
612-
heap_fetch(onerel,SnapshotNow,&targtuple,&targbuffer,NULL);
628+
heap_fetch(onerel,SnapshotNow,&targtuple,&tupbuffer,NULL);
613629
if (targtuple.t_data!=NULL)
614630
{
615631
/*
@@ -621,6 +637,9 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
621637
Assert(k >=0&&k<targrows);
622638
heap_freetuple(rows[k]);
623639
rows[k]=heap_copytuple(&targtuple);
640+
/* this releases the second pin acquired by heap_fetch: */
641+
ReleaseBuffer(tupbuffer);
642+
/* this releases the initial pin: */
624643
ReleaseBuffer(targbuffer);
625644
lastblock=targblock;
626645
lastoffset=targoffset;
@@ -639,7 +658,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
639658
/*
640659
* Estimate total number of valid rows in relation.
641660
*/
642-
*totalrows=(long) (onerel->rd_nblocks*tuplesperpage+0.5);
661+
*totalrows=floor((double)onerel->rd_nblocks*tuplesperpage+0.5);
643662

644663
returnnumrows;
645664
}
@@ -667,6 +686,12 @@ random_fract(void)
667686
* of the last record processed and next record to process. The only extra
668687
* state needed between calls is W, a random state variable.
669688
*
689+
* Note: the original algorithm defines t, S, numer, and denom as integers.
690+
* Here we express them as doubles to avoid overflow if the number of rows
691+
* in the table exceeds INT_MAX. The algorithm should work as long as the
692+
* row count does not become so large that it is not represented accurately
693+
* in a double (on IEEE-math machines this would be around 2^52 rows).
694+
*
670695
* init_selection_state computes the initial W value.
671696
*
672697
* Given that we've already processed t records (t >= n),
@@ -680,36 +705,36 @@ init_selection_state(int n)
680705
returnexp(-log(random_fract())/n);
681706
}
682707

683-
staticlong
684-
select_next_random_record(longt,intn,double*stateptr)
708+
staticdouble
709+
select_next_random_record(doublet,intn,double*stateptr)
685710
{
686711
/* The magic constant here is T from Vitter's paper */
687-
if (t <= (22*n))
712+
if (t <= (22.0*n))
688713
{
689714
/* Process records using Algorithm X until t is large enough */
690715
doubleV,
691716
quot;
692717

693718
V=random_fract();/* Generate V */
694-
t++;
695-
quot= (double) (t-n) / (double)t;
719+
t+=1;
720+
quot= (t-(double)n) /t;
696721
/* Find min S satisfying (4.1) */
697722
while (quot>V)
698723
{
699-
t++;
700-
quot *= (double) (t-n) / (double)t;
724+
t+=1;
725+
quot *= (t-(double)n) /t;
701726
}
702727
}
703728
else
704729
{
705730
/* Now apply Algorithm Z */
706731
doubleW=*stateptr;
707-
longterm=t-n+1;
708-
intS;
732+
doubleterm=t- (double)n+1;
733+
doubleS;
709734

710735
for (;;)
711736
{
712-
longnumer,
737+
doublenumer,
713738
numer_lim,
714739
denom;
715740
doubleU,
@@ -722,9 +747,9 @@ select_next_random_record(long t, int n, double *stateptr)
722747
/* Generate U and X */
723748
U=random_fract();
724749
X=t* (W-1.0);
725-
S=X;/* S is tentatively set to floor(X) */
750+
S=floor(X);/* S is tentatively set to floor(X) */
726751
/* Test if U <= h(S)/cg(X) in the manner of (6.3) */
727-
tmp= (double) (t+1) / (double)term;
752+
tmp= (t+1) /term;
728753
lhs=exp(log(((U*tmp*tmp)* (term+S))/(t+X))/n);
729754
rhs= (((t+X)/(term+S))*term)/t;
730755
if (lhs <=rhs)
@@ -734,20 +759,20 @@ select_next_random_record(long t, int n, double *stateptr)
734759
}
735760
/* Test if U <= f(S)/cg(X) */
736761
y= (((U* (t+1))/term)* (t+S+1))/(t+X);
737-
if (n<S)
762+
if ((double)n<S)
738763
{
739764
denom=t;
740765
numer_lim=term+S;
741766
}
742767
else
743768
{
744-
denom=t-n+S;
769+
denom=t-(double)n+S;
745770
numer_lim=t+1;
746771
}
747-
for (numer=t+S;numer >=numer_lim;numer--)
772+
for (numer=t+S;numer >=numer_lim;numer-=1)
748773
{
749-
y *=(double)numer / (double)denom;
750-
denom--;
774+
y *=numer /denom;
775+
denom-=1;
751776
}
752777
W=exp(-log(random_fract())/n);/* Generate W in advance */
753778
if (exp(log(y)/n) <= (t+X)/t)
@@ -783,30 +808,6 @@ compare_rows(const void *a, const void *b)
783808
return0;
784809
}
785810

786-
/*
787-
* Discover the largest valid tuple offset number on the given page
788-
*
789-
* This code probably ought to live in some other module.
790-
*/
791-
staticOffsetNumber
792-
get_page_max_offset(Relationrelation,BlockNumberblocknumber)
793-
{
794-
Bufferbuffer;
795-
Pagep;
796-
OffsetNumberoffnum;
797-
798-
buffer=ReadBuffer(relation,blocknumber);
799-
if (!BufferIsValid(buffer))
800-
elog(ERROR,"get_page_max_offset: %s relation: ReadBuffer(%ld) failed",
801-
RelationGetRelationName(relation), (long)blocknumber);
802-
LockBuffer(buffer,BUFFER_LOCK_SHARE);
803-
p=BufferGetPage(buffer);
804-
offnum=PageGetMaxOffsetNumber(p);
805-
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
806-
ReleaseBuffer(buffer);
807-
returnoffnum;
808-
}
809-
810811

811812
/*
812813
*compute_minimal_stats() -- compute minimal column statistics
@@ -825,7 +826,7 @@ get_page_max_offset(Relation relation, BlockNumber blocknumber)
825826
*/
826827
staticvoid
827828
compute_minimal_stats(VacAttrStats*stats,
828-
TupleDesctupDesc,longtotalrows,
829+
TupleDesctupDesc,doubletotalrows,
829830
HeapTuple*rows,intnumrows)
830831
{
831832
inti;
@@ -1002,7 +1003,7 @@ compute_minimal_stats(VacAttrStats *stats,
10021003

10031004
if (f1<1)
10041005
f1=1;
1005-
term1=sqrt((double)totalrows / (double)numrows)*f1;
1006+
term1=sqrt(totalrows / (double)numrows)*f1;
10061007
stats->stadistinct=floor(term1+nmultiple+0.5);
10071008
}
10081009

@@ -1104,7 +1105,7 @@ compute_minimal_stats(VacAttrStats *stats,
11041105
*/
11051106
staticvoid
11061107
compute_scalar_stats(VacAttrStats*stats,
1107-
TupleDesctupDesc,longtotalrows,
1108+
TupleDesctupDesc,doubletotalrows,
11081109
HeapTuple*rows,intnumrows)
11091110
{
11101111
inti;
@@ -1298,7 +1299,7 @@ compute_scalar_stats(VacAttrStats *stats,
12981299

12991300
if (f1<1)
13001301
f1=1;
1301-
term1=sqrt((double)totalrows / (double)numrows)*f1;
1302+
term1=sqrt(totalrows / (double)numrows)*f1;
13021303
stats->stadistinct=floor(term1+nmultiple+0.5);
13031304
}
13041305

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