Add an optimization control bit to disable the OP_SeekScan optimization.

FossilOrigin-Name: f674c41e5cbbb08ffc3cc00ab449229b672054c872e209337f12e7eacb531fe5

manifest

@@ -1,5 +1,5 @@
-C Fix\san\sALWAYS\swhich\scan\sbe\sfalse.
-D 2021-06-02T18:50:39.413
+C Add\san\soptimization\scontrol\sbit\sto\sdisable\sthe\sOP_SeekScan\soptimization.
+D 2021-06-02T19:28:07.128
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -549,7 +549,7 @@ F src/shell.c.in 2a2b06d463933ee3a5bb0242d5d2200ca36769493fd6f4d939a0574113f3d6d
 F src/sqlite.h.in 5c950066775ca9efdaa49077c05d38d0bef6418f3bd07d2dce0210f1d2f3c326
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 61b38c073d5e1e96a3d45271b257aef27d0d13da2bea5347692ae579475cd95e
-F src/sqliteInt.h 6d0c49ed218f9f6ffabfdc8bed1a5de89f61e70c96a62156aeebeb20c1be9bf0
+F src/sqliteInt.h de7cf989dad75a3287a8b486083b21149bdead3669794b5a9c7e331668443ae1
 F src/sqliteLimit.h d7323ffea5208c6af2734574bae933ca8ed2ab728083caa117c9738581a31657
 F src/status.c 4b8bc2a6905163a38b739854a35b826c737333fab5b1f8e03fa7eb9a4799c4c1
 F src/table.c 0f141b58a16de7e2fbe81c308379e7279f4c6b50eb08efeec5892794a0ba30d1
@@ -631,7 +631,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c c8ec20a1ca161d5635a4f19c2a4efec2e006e19a8a61f272bf6bce1c80ab7436
 F src/wal.h c3aa7825bfa2fe0d85bef2db94655f99870a285778baa36307c0a16da32b226a
 F src/walker.c 7342becedf3f8a26f9817f08436bdf8b56ad69af83705f6b9320a0ad3092c2ac
-F src/where.c fbb2da2b618c4a382a803d2a68795ade50702fa1cc21cd7c5b42f48ce811050a
+F src/where.c dc062832c30aa6c5f17805c1235b2b621cd9db506412d5d3ef0799d26ae3396f
 F src/whereInt.h 9248161dd004f625ce5d3841ca9b99fed3fc8d61522cf76340fc5217dbe1375b
 F src/wherecode.c 9f1f65d11437b25cd0a1497a170514c785f19ce6ad9d3e6fc73719cb5a49012f
 F src/whereexpr.c 5a9c9f5d2dac4bcdcaae3035034b4667523f731df228e0bb1d4efc669efa9da5
@@ -1918,7 +1918,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P dbc33d3ae30de5427a4351824a11026145f778fad95bd0b825bd0a4b63059677
-R f9344dd18f4fb48d394c285c581c4451
+P a87f8ecd6db11ea40a15314b875fc78289c19ab2dec6f738b4bf37f4aafa7bbd
+R 0673ef2c1144007e5dc9919859a8d932
 U drh
-Z dd1ede918ea9d283fd53a1c6a619c45c
+Z e77ba6d1357c1434f617cbb216a877e4

manifest.uuid

@@ -1 +1 @@
-a87f8ecd6db11ea40a15314b875fc78289c19ab2dec6f738b4bf37f4aafa7bbd
+f674c41e5cbbb08ffc3cc00ab449229b672054c872e209337f12e7eacb531fe5

src/sqliteInt.h

@@ -1731,6 +1731,7 @@ struct sqlite3 {
 #define SQLITE_SkipScan       0x00004000 /* Skip-scans */
 #define SQLITE_PropagateConst 0x00008000 /* The constant propagation opt */
 #define SQLITE_MinMaxOpt      0x00010000 /* The min/max optimization */
+#define SQLITE_SeekScan       0x00020000 /* The OP_SeekScan optimization */
 #define SQLITE_AllOpts        0xffffffff /* All optimizations */
 
 /*

src/where.c

@@ -2627,7 +2627,7 @@ static int whereLoopAddBtreeIndex(
             ("IN operator (N=%d M=%d logK=%d nIn=%d rLogSize=%d x=%d) "
              "prefers indexed lookup\n",
              saved_nEq, M, logK, nIn, rLogSize, x));
-        }else if( nInMul<2 ){
+        }else if( nInMul<2 && OptimizationEnabled(db, SQLITE_SeekScan) ){
           WHERETRACE(0x40,
             ("IN operator (N=%d M=%d logK=%d nIn=%d rLogSize=%d x=%d"
              " nInMul=%d) prefers skip-scan\n",