Revisiting the IN-scan optimization to try to fix it for the corner case

where the statistics deceive the query planner into using a scan when
an indexed lookup would be better.  This check-in changes the code
generation to do the IN-scan using a new OP_SeekScan opcode.  That new
opcode is designed to abandon the scan and fall back to a seek if
it doesn't find a match quickly enough.  For this work-in-progress check-in,
OP_SeekScan is still a no-op and OP_SeekGE still ends up doing all the work.

FossilOrigin-Name: d720b6981eeb0ffdb14494ca63eca298ee724ae4ad4863c7c7cbfdad7fa52519

diff --git a/manifest b/manifest
index 96eacb42aedb809ebed1a6799e448e31a924a2ac..4e0a60c8823a7e6df6dfddc2c4c1006b57a23501 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Small\sperformance\simprovement\sand\ssize\sreduction\sby\sreducing\sthe\ssize\sof\nthe\sWhereTerm\sobject.
-D 2020-09-28T15:49:43.021
+C Revisiting\sthe\sIN-scan\soptimization\sto\stry\sto\sfix\sit\sfor\sthe\scorner\scase\nwhere\sthe\sstatistics\sdeceive\sthe\squery\splanner\sinto\susing\sa\sscan\swhen\nan\sindexed\slookup\swould\sbe\sbetter.\s\sThis\scheck-in\schanges\sthe\scode\ngeneration\sto\sdo\sthe\sIN-scan\susing\sa\snew\sOP_SeekScan\sopcode.\s\sThat\snew\nopcode\sis\sdesigned\sto\sabandon\sthe\sscan\sand\sfall\sback\sto\sa\sseek\sif\nit\sdoesn't\sfind\sa\smatch\squickly\senough.\s\sFor\sthis\swork-in-progress\scheck-in,\s\nOP_SeekScan\sis\sstill\sa\sno-op\sand\sOP_SeekGE\sstill\sends\sup\sdoing\sall\sthe\swork.
+D 2020-09-28T19:51:54.673
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -607,7 +607,7 @@ F src/upsert.c 2920de71b20f04fe25eb00b655d086f0ba60ea133c59d7fa3325c49838818e78
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c c0c7977de7ef9b8cb10f6c85f2d0557889a658f817b0455909a49179ba4c8002
 F src/vacuum.c 492422c1463c076473bae1858799c7a0a5fe87a133d1223239447c422cd26286
-F src/vdbe.c 6430a540012b8b4c81076565804fcb979040e1b1a43ce76d2381863884155d84
+F src/vdbe.c 17584029ae2c2acc955f3dc19858fad1a3d509f31d42ddd2ff7be3552d4c77d3
 F src/vdbe.h 83603854bfa5851af601fc0947671eb260f4363e62e960e8a994fb9bbcd2aaa1
 F src/vdbeInt.h 3ca5e9fd6e095a8b6cf6bc3587a46fc93499503b2fe48951e1034ba9e2ce2f6e
 F src/vdbeapi.c c5e7cb2ab89a24d7f723e87b508f21bfb1359a04db5277d8a99fd1e015c12eb9
@@ -622,9 +622,9 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 69e770e96fd56cc21608992bf2c6f1f3dc5cf2572d0495c6a643b06c3a679f14
 F src/wal.h c3aa7825bfa2fe0d85bef2db94655f99870a285778baa36307c0a16da32b226a
 F src/walker.c 3df26a33dc4f54e8771600fb7fdebe1ece0896c2ad68c30ab40b017aa4395049
-F src/where.c 7ed6512e73e679231ebdeba470055e8d8e871a020b7f3f8dc75e993aaebdcbcd
-F src/whereInt.h db7472b6eb617b5853ae74bbd755383e2275be72ae03ff07cc8ea141bb146dc8
-F src/wherecode.c 895ff782a62370a823c99dc7e1bca09ffd90392c9fafc007b6d3df4811e88b4f
+F src/where.c c628a6850b023cfacfdbf6060481eae5e538ccb3c3464a700b501e08d4cce74b
+F src/whereInt.h 59077fbd0b3d01bc8715e746c86a99ebf4c85bde8a57077ec04d2a23e59666ec
+F src/wherecode.c 4096498d05f0c1bfff435ef48679e774a345bb2c700215da1383902e14877d5c
 F src/whereexpr.c 2a05552e808047a93845278c98c6ca64a265fa8e9ffd087c161bb11bfe339866
 F src/window.c edd6f5e25a1e8f2b6f5305b7f5f7da7bb35f07f0d432b255b1d4c2fcab4205aa
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
@@ -1880,7 +1880,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d3d13df31a97648f952beb2e1a783f947a80ec843227985ad9ebd14452d2f654
-R 7b8c3cb46dfe068597bdde1b75906671
+P 43f7ddad800acf40917c5cc3d926640dbec17c34d5f1cbbb74bd80f44eeed0a5
+R 91153af0a9416b3fbb7b5420545d1fbb
+T *branch * in-scan-vs-index
+T *sym-in-scan-vs-index *
+T -sym-trunk *
 U drh
-Z d72bcf93f915317cb95885e250422e3c
+Z 22384fb99540c2e7915964a3edd63b6d

diff --git a/manifest.uuid b/manifest.uuid
index f071ea53f693f5b4474573e48b50a1cd25ca3bd5..0ba7bb60dcf097a95b347728ad59d3b866327576 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-43f7ddad800acf40917c5cc3d926640dbec17c34d5f1cbbb74bd80f44eeed0a5
\ No newline at end of file
+d720b6981eeb0ffdb14494ca63eca298ee724ae4ad4863c7c7cbfdad7fa52519
\ No newline at end of file

diff --git a/src/vdbe.c b/src/vdbe.c
index a579b4ea119d0422dcebb31e99d9a2c210867f08..d14838e4f189f7d3b6b3a3f82fcd4d0e73a4505d 100644 (file)
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -4383,6 +4383,59 @@ seek_not_found:
   break;
 }
 
+
+/* Opcode: SeekScan
+** Synopsis: Scan-ahead up to P1 rows
+**
+** This opcode is a prefix.  It must be followed immediately by
+** OP_SeekGE and then OP_IdxGT.  This opcode should occur in no other
+** context.  That constraint is verified using assert() statements in
+** the code.
+**
+** This opcode helps to optimize IN operators on a multi-column index
+** where the IN operator is on the later terms of the index.
+**
+** The P3 and P4 operations of the OP_SeekGE opcode that follows this
+** opcode identify an unpacked key which is the desired entry that
+** we want to advance the cursor to.  Call this the "target".
+**
+** If the OP_SeekGE opcode that immediately follows this opcode has
+** never run before, then this opcode is a no-op and control passes
+** through into the OP_SeekGE.
+**
+** If the subsequent OP_SeekGE opcode has run before, then that prior
+** might OP_SeekGE might have left the cursor pointing any entry that
+** is close to the target.  This routine checks, and if possible
+** bypasses the OP_SeekGE.
+**
+** If the cursor is past the target, jump immediately to the
+** P2 of the subsequent OP_SeekGE.
+**
+** If the cursor is less than the target, then step forward up to P1
+** times trying to find a match.  If during these steps, the
+** cursor moves past the target, then jump immediately to
+** the P2 of the subsequent OP_SeekGE.  If a match is found, jump
+** to the first instruction past the OP_IdxGT that follows the
+** OP_SeekGE.  (In other words, skip over the next two opcodes).
+** If P1 steps are performed and the cursor is still less than the
+** target, then fall through into OP_SeekGE opcode.
+**
+** This opcode is an optimization.  This opcode can be a no-op and
+** the correct answer should still be obtained.  The purpose of this
+** opcode is to bypass unnecessary OP_SeekGE operations.
+*/
+case OP_SeekScan: {
+  assert( pOp[1].opcode==OP_SeekGE );
+  assert( pOp[2].opcode==OP_IdxGT );
+  assert( pOp[1].p1==pOp[2].p1 );
+  assert( pOp[1].p2==pOp[2].p2 );
+  assert( pOp[1].p3==pOp[2].p3 );
+  assert( pOp[1].p4.i==pOp[2].p4.i );
+  assert( pOp->p1>0 );
+  break;  /* No-op for now.  FIX ME. */
+}
+
+
 /* Opcode: SeekHit P1 P2 P3 * *
 ** Synopsis: set P2<=seekHit<=P3
 **

diff --git a/src/where.c b/src/where.c
index 9049a59f283c1bc683626618960739d1af89e3db..0ab5adee8fc7a8188d5863c273e29de1434783ad 100644 (file)
--- a/src/where.c
+++ b/src/where.c
@@ -2564,7 +2564,7 @@ static int whereLoopAddBtreeIndex(
           WHERETRACE(0x40,
             ("Scan preferred over IN operator on column %d of \"%s\" (%d<%d)\n",
              saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));
-          continue;
+          pNew->wsFlags |= WHERE_IN_SEEKSCAN;
         }else{
           WHERETRACE(0x40,
             ("IN operator preferred on column %d of \"%s\" (%d>=%d)\n",
@@ -5197,6 +5197,7 @@ WhereInfo *sqlite3WhereBegin(
         if( (pLoop->wsFlags & WHERE_CONSTRAINT)!=0
          && (pLoop->wsFlags & (WHERE_COLUMN_RANGE|WHERE_SKIPSCAN))==0
          && (pLoop->wsFlags & WHERE_BIGNULL_SORT)==0
+         && (pLoop->wsFlags & WHERE_IN_SEEKSCAN)==0
          && (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)==0
          && pWInfo->eDistinct!=WHERE_DISTINCT_ORDERED
         ){

diff --git a/src/whereInt.h b/src/whereInt.h
index 0a2b5c5cefe3c87b8a4a649581cc4abd531be25e..6c969af9c2c262a337f84be6c58d7ef2b479549f 100644 (file)
--- a/src/whereInt.h
+++ b/src/whereInt.h
@@ -619,5 +619,6 @@ void sqlite3WhereTabFuncArgs(Parse*, struct SrcList_item*, WhereClause*);
 #define WHERE_PARTIALIDX   0x00020000  /* The automatic index is partial */
 #define WHERE_IN_EARLYOUT  0x00040000  /* Perhaps quit IN loops early */
 #define WHERE_BIGNULL_SORT 0x00080000  /* Column nEq of index is BIGNULL */
+#define WHERE_IN_SEEKSCAN  0x00100000  /* Seek-scan optimization for IN */
 
 #endif /* !defined(SQLITE_WHEREINT_H) */

diff --git a/src/wherecode.c b/src/wherecode.c
index e3310b314e8f8370fe53eb0dca2a8099573dbe84..8227d0d7d0c3d804a2b5fd010d543f8ab6e49ce2 100644 (file)
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -1804,6 +1804,11 @@ Bitmask sqlite3WhereCodeOneLoopStart(
 
       op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
       assert( op!=0 );
+      if( (pLoop->wsFlags & WHERE_IN_SEEKSCAN)!=0 ){
+        assert( op==OP_SeekGE );
+        assert( regBignull==0 );
+        sqlite3VdbeAddOp1(v, OP_SeekScan, 10);
+      }
       sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
       VdbeCoverage(v);
       VdbeCoverageIf(v, op==OP_Rewind);  testcase( op==OP_Rewind );