mirror of https://github.com/sqlite/sqlite
Use histogram data to improve the row-count estimates on equality constraints.
FossilOrigin-Name: 6bfc5c69eb22938972bbf4e60179952dc215f770
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drh
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24
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@ -1,8 +1,8 @@
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-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA1
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C The\sfirst\sof\sa\splanned\sseries\sof\senhancements\sto\sthe\squery\splanner\sthat\nenable\sit\sto\smake\sbetter\suse\sof\ssqlite_stat2\shistograms\swhen\sthe\stable\nhas\smany\srepeated\svalues.
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D 2011-01-20T02:56:37.736
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C Use\shistogram\sdata\sto\simprove\sthe\srow-count\sestimates\son\sequality\sconstraints.
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D 2011-01-20T16:52:09.439
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F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
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F Makefile.in de6498556d536ae60bb8bb10e8c1ba011448658c
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F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
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@ -243,7 +243,7 @@ F src/vtab.c b297e8fa656ab5e66244ab15680d68db0adbec30
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F src/wal.c dbca424f71678f663a286ab2a98f947af1d412a7
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F src/wal.h c1aac6593a0b02b15dc625987e619edeab39292e
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F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
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F src/where.c 5cd6b88d57bfc816ba7f753a3cdf03686d954b8a
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F src/where.c 068ecc5195578aed083a4314e572de9979a489e5
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F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
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F test/alias.test 4529fbc152f190268a15f9384a5651bbbabc9d87
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F test/all.test 51756962d522e474338e9b2ebb26e7364d4aa125
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@ -256,7 +256,7 @@ F test/analyze.test c1eb87067fc16ece7c07e823d6395fd831b270c5
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F test/analyze2.test f45ac8d54bdad822139e53fc6307fc6b5ee41c69
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F test/analyze3.test 820ddfb7591b49607fbaf77240c7955ac3cabb04
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F test/analyze4.test 757b37875cf9bb528d46f74497bc789c88365045
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F test/analyze5.test 18987796646efdf009ca0b8c8f060874a8fe57fb
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F test/analyze5.test b6bd2e4fbbe2ffcf2a22250b28fb1f2a2ca507de
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F test/async.test ad4ba51b77cd118911a3fe1356b0809da9c108c3
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F test/async2.test bf5e2ca2c96763b4cba3d016249ad7259a5603b6
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F test/async3.test 93edaa9122f498e56ea98c36c72abc407f4fb11e
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@ -900,18 +900,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
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F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
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F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
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F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
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P 9660a0a22547656cc3765b673d0cee9e1dd829ef
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R 9ff1bb21abd03a28e074b829beb25c52
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T *bgcolor * #a8c7d3
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T *branch * stat2-enhancement
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T *sym-stat2-enhancement *
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T -sym-trunk *
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P 2cd374cd23fa2fd38f49090d6eeb9b1e521d51d5
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R b298fdc0ea4be4264436dd1639cb2644
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U drh
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Z 10e84b987d0709faa336295530a6ebae
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@ -1 +1 @@
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2cd374cd23fa2fd38f49090d6eeb9b1e521d51d5
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6bfc5c69eb22938972bbf4e60179952dc215f770
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68
src/where.c
68
src/where.c
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@ -2461,6 +2461,51 @@ range_est_fallback:
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return rc;
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}
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#ifdef SQLITE_ENABLE_STAT2
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/*
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** Estimate the number of rows that will be returned based on
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** an equality constraint x=VALUE and where that VALUE occurs in
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** the histogram data. This only works when x is the left-most
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** column of an index and sqlite_stat2 histogram data is available
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** for that index.
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**
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** Write the estimated row count into *pnRow. If unable to make
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** an estimate, leave *pnRow unchanged.
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*/
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void whereEqScanEst(
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Parse *pParse, /* Parsing & code generating context */
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Index *p, /* The index whose left-most column is pTerm */
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WhereTerm *pTerm, /* The x=VALUE constraint */
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double *pnRow /* Write the revised row estimate here */
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){
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sqlite3_value *pRhs = 0; /* VALUE on right-hand side of pTerm */
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int iLower, iUpper; /* Range of histogram regions containing pRhs */
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u8 aff; /* Column affinity */
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int rc; /* Subfunction return code */
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double nRowEst; /* New estimate of the number of rows */
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assert( p->aSample!=0 );
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assert( pTerm->eOperator==WO_EQ );
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aff = p->pTable->aCol[p->aiColumn[0]].affinity;
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rc = valueFromExpr(pParse, pTerm->pExpr->pRight, aff, &pRhs);
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if( rc ) goto whereEqScanEst_cancel;
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rc = whereRangeRegion(pParse, p, pRhs, 0, &iLower);
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if( rc ) goto whereEqScanEst_cancel;
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rc = whereRangeRegion(pParse, p, pRhs, 1, &iUpper);
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if( rc ) goto whereEqScanEst_cancel;
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if( iLower>=iUpper ){
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nRowEst = p->aiRowEst[0]/(SQLITE_INDEX_SAMPLES*2);
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if( nRowEst<*pnRow ) *pnRow = nRowEst;
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}else{
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nRowEst = (iUpper-iLower)*p->aiRowEst[0]/SQLITE_INDEX_SAMPLES;
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*pnRow = nRowEst;
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}
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whereEqScanEst_cancel:
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sqlite3ValueFree(pRhs);
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}
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#endif /* defined(SQLITE_ENABLE_STAT2) */
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/*
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** Find the query plan for accessing a particular table. Write the
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@ -2624,10 +2669,13 @@ static void bestBtreeIndex(
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int bInEst = 0;
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int nInMul = 1;
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int estBound = 100;
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int nBound = 0; /* Number of range constraints seen */
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int nBound = 0; /* Number of range constraints seen */
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int bSort = 0;
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int bLookup = 0;
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WhereTerm *pTerm; /* A single term of the WHERE clause */
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WhereTerm *pTerm; /* A single term of the WHERE clause */
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#ifdef SQLITE_ENABLE_STAT2
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WhereTerm *pFirstEqTerm = 0; /* First WO_EQ term */
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#endif
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/* Determine the values of nEq and nInMul */
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for(nEq=0; nEq<pProbe->nColumn; nEq++){
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}else if( pTerm->eOperator & WO_ISNULL ){
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wsFlags |= WHERE_COLUMN_NULL;
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}
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#ifdef SQLITE_ENABLE_STAT2
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else if( nEq==0 && pProbe->aSample ){
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pFirstEqTerm = pTerm;
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}
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#endif
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used |= pTerm->prereqRight;
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}
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@ -2723,6 +2776,17 @@ static void bestBtreeIndex(
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nInMul = (int)(nRow / aiRowEst[nEq]);
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}
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#ifdef SQLITE_ENABLE_STAT2
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/* If the constraint is of the form x=VALUE and histogram
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** data is available for column x, then it might be possible
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** to get a better estimate on the number of rows based on
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** VALUE and how common that value is according to the histogram.
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*/
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if( nRow>(double)1 && nEq==1 && pFirstEqTerm!=0 ){
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whereEqScanEst(pParse, pProbe, pFirstEqTerm, &nRow);
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}
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#endif /* SQLITE_ENABLE_STAT2 */
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/* Assume constant cost to access a row and logarithmic cost to
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** do a binary search. Hence, the initial cost is the number of output
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** rows plus log2(table-size) times the number of binary searches.
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@ -214,6 +214,14 @@ foreach {testid where rows} {
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20 {y>=0 AND y<'charlie'} 700
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21 {y>=0 AND y<='charlie'} 900
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22 {y>=0 AND y<'delta'} 900
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23 {y>'alpha' AND y<x'00'} 600
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24 {y>='bravo' AND y<x'00'} 600
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25 {y>'bravo' AND y<x'00'} 300
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26 {y>='charlie' AND y<x'00'} 300
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27 {y>'charlie' AND y<x'00'} 100
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28 {y>='delta' AND y<x'00'} 100
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29 {y>'delta' AND y<x'00'} 50
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30 {y>='echo' AND y<x'00'} 50
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} {
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do_test analyze5-3.$testid {
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eqp "SELECT * FROM t1 WHERE $where"
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