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Adjust skip-scan cost estimates slightly so that a full table scan is

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preferred over a skip-scan to a column with only two distinct values.

FossilOrigin-Name: ae9a42b268ad3f7d21a5813bb931e795c6917014
This commit is contained in:
drh 2014-09-23 01:40:59 +00:00
parent a4bb5b0726
commit 14f0e2128a
5 changed files with 41 additions and 16 deletions

16
manifest

@ -1,5 +1,5 @@
C Fix\sto\spayload\ssize\soverflow\sdetection\sin\sthe\scellSizePtr()\schange\sof\nthe\sprevious\scheck-in.
D 2014-09-22T20:38:10.316
C Adjust\sskip-scan\scost\sestimates\sslightly\sso\sthat\sa\sfull\stable\sscan\sis\npreferred\sover\sa\sskip-scan\sto\sa\scolumn\swith\sonly\stwo\sdistinct\svalues.
D 2014-09-23T01:40:59.122
F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
F Makefile.in cf57f673d77606ab0f2d9627ca52a9ba1464146a
F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@ -302,7 +302,7 @@ F src/vtab.c 019dbfd0406a7447c990e1f7bd1dfcdb8895697f
F src/wal.c 10e7de7ce90865a68153f001a61f1d985cd17983
F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
F src/walker.c c253b95b4ee44b21c406e2a1052636c31ea27804
F src/where.c 3f859ecfada8643ce8255f20d481b5a3e0921662
F src/where.c a14d3d8042adeb51f81731c1b47b3e481d1cc23a
F src/whereInt.h 124d970450955a6982e174b07c320ae6d62a595c
F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
@ -836,10 +836,10 @@ F test/shortread1.test bb591ef20f0fd9ed26d0d12e80eee6d7ac8897a3
F test/show_speedtest1_rtree.tcl 32e6c5f073d7426148a6936a0408f4b5b169aba5
F test/shrink.test 8c70f62b6e8eb4d54533de6d65bd06b1b9a17868
F test/sidedelete.test f0ad71abe6233e3b153100f3b8d679b19a488329
F test/skipscan1.test 28c7faa41a0d7265040ecb0a0abd90c0904270b2
F test/skipscan1.test 7e15e1cc524524e7b2c4595ec85c75501d22f4ff
F test/skipscan2.test d1d1450952b7275f0b0a3a981f0230532743951a
F test/skipscan3.test ec5bab3f81c7038b43450e7b3062e04a198bdbb5
F test/skipscan5.test d8b9692b702745a0e41c23f9da6beac81df01196
F test/skipscan5.test 67817a4b6857c47e0e33ba3e506da6f23ef68de2
F test/soak.test 0b5b6375c9f4110c828070b826b3b4b0bb65cd5f
F test/softheap1.test 40562fe6cac6d9827b7b42b86d45aedf12c15e24
F test/sort.test 15e1d3014abc3f6d4357ed81b93b82117aefd235
@ -1199,7 +1199,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
P bc8bbf3207288d160287519c3b7123997996b440
R 5a3408a8ae29b6451a1037ab47048e78
P 7609744014c6a84a8379794a0351a2e9626ec86b
R cb94e4a1db7c56387373fb77d2698ee3
U drh
Z 93e96edbb124ae02212644cc0f189540
Z a13a3c1c4006b80e078cd097de2cdb1a

2
manifest.uuid

@ -1 +1 @@
7609744014c6a84a8379794a0351a2e9626ec86b
ae9a42b268ad3f7d21a5813bb931e795c6917014

5
src/where.c

@ -4359,11 +4359,14 @@ static int whereLoopAddBtreeIndex(
nIter = pProbe->aiRowLogEst[saved_nEq] - pProbe->aiRowLogEst[saved_nEq+1];
if( pTerm ){
/* TUNING: When estimating skip-scan for a term that is also indexable,
** increase the cost of the skip-scan by 2x, to make it a little less
** multiply the cost of the skip-scan by 2.0, to make it a little less
** desirable than the regular index lookup. */
nIter += 10; assert( 10==sqlite3LogEst(2) );
}
pNew->nOut -= nIter;
/* TUNING: Because uncertainties in the estimates for skip-scan queries,
** add a 1.375 fudge factor to make skip-scan slightly less likely. */
nIter += 5;
whereLoopAddBtreeIndex(pBuilder, pSrc, pProbe, nIter + nInMul);
pNew->nOut = saved_nOut;
pNew->u.btree.nEq = saved_nEq;

28
test/skipscan1.test

@ -245,6 +245,32 @@ do_execsql_test skipscan1-5.3 {
SELECT xh, loc FROM t5 WHERE loc >= 'M' AND loc < 'N';
} {/.*COVERING INDEX t5i1 .*/}
# The column used by the skip-scan needs to be sufficiently selective.
# See the private email from Adi Zaimi to drh@sqlite.org on 2014-09-22.
#
db close
forcedelete test.db
sqlite3 db test.db
do_execsql_test skipscan1-6.1 {
CREATE TABLE t1(a,b,c,d,e,f,g,h varchar(300));
CREATE INDEX t1ab ON t1(a,b);
ANALYZE sqlite_master;
-- Only two distinct values for the skip-scan column. Skip-scan is not used.
INSERT INTO sqlite_stat1 VALUES('t1','t1ab','500000 250000 125000');
ANALYZE sqlite_master;
EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {~/ANY/}
do_execsql_test skipscan1-6.2 {
-- Four distinct values for the skip-scan column. Skip-scan is used.
UPDATE sqlite_stat1 SET stat='500000 250000 62500';
ANALYZE sqlite_master;
EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {/ANY.a. AND b=/}
do_execsql_test skipscan1-6.3 {
-- Two distinct values for the skip-scan column again. Skip-scan is not used.
UPDATE sqlite_stat1 SET stat='500000 125000 62500';
ANALYZE sqlite_master;
EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {~/ANY/}
finish_test

6
test/skipscan5.test

@ -108,7 +108,7 @@ foreach {tn dbenc coll} {
3 { c > 'q' } {/*ANY(a) AND ANY(b) AND c>?*/}
4 { c > 'e' } {/*SCAN TABLE t2*/}
5 { c < 'q' } {/*SCAN TABLE t2*/}
4 { c < 'e' } {/*ANY(a) AND ANY(b) AND c<?*/}
6 { c < 'c' } {/*ANY(a) AND ANY(b) AND c<?*/}
} {
set sql "EXPLAIN QUERY PLAN SELECT * FROM t2 WHERE $q"
do_execsql_test 2.$tn.$tn2 $sql $res
@ -180,7 +180,3 @@ foreach {tn q res} {
}
finish_test