From: dan <dan@noemail.net>
Date: Wed, 30 Apr 2014 15:00:16 +0000 (+0000)
Subject: Add text to the header comment of whereLoopAddBtree() describing how the costs of... 
X-Git-Tag: version-3.8.5~65^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fheads%2Fexperimental-costs;p=thirdparty%2Fsqlite.git

Add text to the header comment of whereLoopAddBtree() describing how the costs of various b-tree loops are estimated.

FossilOrigin-Name: 05e6e16cb28c9ffb4596bd2ef81f687c5403ecbb
---

diff --git a/manifest b/manifest
index 9f27ec6f9b..35f78b46c2 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Update\sa\scouple\sof\stest\scases\sto\saccount\sfor\sthe\sfact\sthat\sthis\sbranch\sprefers\san\sindex\sscan\sand\spartial\ssort\sover\sa\sfull-table\sscan\sand\sfull\sexternal\ssort.
-D 2014-04-30T14:53:21.345
+C Add\stext\sto\sthe\sheader\scomment\sof\swhereLoopAddBtree()\sdescribing\show\sthe\scosts\sof\svarious\sb-tree\sloops\sare\sestimated.
+D 2014-04-30T15:00:16.197
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 2ef13430cd359f7b361bb863504e227b25cc7f81
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -292,7 +292,7 @@ F src/vtab.c 21b932841e51ebd7d075e2d0ad1415dce8d2d5fd
 F src/wal.c 76e7fc6de229bea8b30bb2539110f03a494dc3a8
 F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
 F src/walker.c 11edb74d587bc87b33ca96a5173e3ec1b8389e45
-F src/where.c e91b92908c973b2b6b03145dcd131a8ca8b1bf64
+F src/where.c 4aeb1caa0a16c76e0c0566af4c64ba003836a0aa
 F src/whereInt.h 6804c2e5010378568c2bb1350477537755296a46
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
@@ -1166,7 +1166,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P eefeda32d54efbbdf7d20b719299eda48b891fae
-R 50e654a1c0b26308b8a927bcd26c6421
+P 9b975bf33cd8fc28c64183a9642bf9fb436a4746
+R 20e49e26218874ddfe5fb9438df8f580
 U dan
-Z f4d62e136a5d6e05753f5050c6fb0c4a
+Z c1e32968c738a6da213a45755f91539c
diff --git a/manifest.uuid b/manifest.uuid
index 00e612df5f..6ee1deefef 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-9b975bf33cd8fc28c64183a9642bf9fb436a4746
\ No newline at end of file
+05e6e16cb28c9ffb4596bd2ef81f687c5403ecbb
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index ec7a908b1a..7d01db61ee 100644
--- a/src/where.c
+++ b/src/where.c
@@ -4349,6 +4349,29 @@ static int whereUsablePartialIndex(int iTab, WhereClause *pWC, Expr *pWhere){
 ** Add all WhereLoop objects for a single table of the join where the table
 ** is idenfied by pBuilder->pNew->iTab.  That table is guaranteed to be
 ** a b-tree table, not a virtual table.
+**
+** The costs (WhereLoop.rRun) of the b-tree loops added by this function
+** are calculated as follows:
+**
+** For a full scan, assuming the table (or index) contains nRow rows:
+**
+**     cost = nRow * 3.0                    // full-table scan
+**     cost = nRow * K                      // scan of covering index
+**     cost = nRow * (K+3.0)                // scan of non-covering index
+**
+** where K is a value between 1.1 and 3.0 set based on the relative 
+** estimated average size of the index and table records.
+**
+** For an index scan, where nVisit is the number of index rows visited
+** by the scan, and nSeek is the number of seek operations required on 
+** the index b-tree:
+**
+**     cost = nSeek * (log(nRow) + K * nVisit)          // covering index
+**     cost = nSeek * (log(nRow) + (K+3.0) * nVisit)    // non-covering index
+**
+** Normally, nSeek is 1. nSeek values greater than 1 come about if the 
+** WHERE clause includes "x IN (....)" terms used in place of "x=?". Or when 
+** implicit "x IN (SELECT x FROM tbl)" terms are added for skip-scans.
 */
 static int whereLoopAddBtree(
   WhereLoopBuilder *pBuilder, /* WHERE clause information */