From c2bb3282f18d90e77e461e5dd203a32a7d6bbf48 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Sun, 4 Sep 2011 01:11:46 +0000
Subject: [PATCH] Improve the testability of the merge-sort logic.

FossilOrigin-Name: b5179baf87aa00ed5cecbdcaa65bee10e112a9e9
---
 manifest       | 14 +++++++-------
 manifest.uuid  |  2 +-
 src/select.c   |  2 +-
 src/vdbesort.c | 24 +++++++++++++++---------
 4 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/manifest b/manifest
index 0291313011..fff4ed9132 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Performance\simprovements\sto\sthe\sexternal\smerge-sorter.\s\sKeep\scontent\son\san\nin-memory\slinked\slists\srather\sthan\san\sephemeral\stable\sprior\sto\sspilling\sto\ndisk.\s\sUse\sthe\sexternal\smerge-sorter\sto\simplement\sORDER\sBY\sand\sGROUP\sBY\nin\saddition\sto\sCREATE\sINDEX.
-D 2011-09-03T17:07:26.674
+C Improve\sthe\stestability\sof\sthe\smerge-sort\slogic.
+D 2011-09-04T01:11:46.977
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in d314143fa6be24828021d3f583ad37d9afdce505
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -179,7 +179,7 @@ F src/printf.c 585a36b6a963df832cfb69505afa3a34ed5ef8a1
 F src/random.c cd4a67b3953b88019f8cd4ccd81394a8ddfaba50
 F src/resolve.c 36368f44569208fa074e61f4dd0b6c4fb60ca2b4
 F src/rowset.c 69afa95a97c524ba6faf3805e717b5b7ae85a697
-F src/select.c 32d0f4e5513362706b8973e7f1b87cd0885dfbf5
+F src/select.c bf7b7ea6befb483619da5f597b0864668b828c3c
 F src/shell.c bbe7818ff5bc8614105ceb81ad67b8bdc0b671dd
 F src/sqlite.h.in 0a6c9c23337fd1352c5c75a613ff9533aa7d91cb
 F src/sqlite3ext.h 1a1a4f784aa9c3b00edd287940197de52487cd93
@@ -245,7 +245,7 @@ F src/vdbeapi.c 11dc47987abacb76ad016dcf5abc0dc422482a98
 F src/vdbeaux.c e58acbc5ea3823922a0cd8fa21f94f39af51ee88
 F src/vdbeblob.c f024f0bf420f36b070143c32b15cc7287341ffd3
 F src/vdbemem.c 5e6effb96dd53d233361cbfaa3f0a43b9af689e9
-F src/vdbesort.c e6d6f0c2aa003f7cbdea8c9be47a15a8e854fb97
+F src/vdbesort.c 4ceadaa20c2a428ea2a5066f6d7d91d7a8118077
 F src/vdbetrace.c 5d0dc3d5fd54878cc8d6d28eb41deb8d5885b114
 F src/vtab.c 901791a47318c0562cd0c676a2c6ff1bc530e582
 F src/wal.c 3154756177d6219e233d84291d5b05f4e06ff5e9
@@ -961,7 +961,7 @@ F tool/symbols.sh caaf6ccc7300fd43353318b44524853e222557d5
 F tool/tostr.awk e75472c2f98dd76e06b8c9c1367f4ab07e122d06
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
 F tool/warnings.sh b7fdb2cc525f5ef4fa43c80e771636dd3690f9d2
-P 61bda876af6df3170263d41d2933168305de58d2 99e34bdce4ccca15b79159b03b96787e7a7ff85b
-R da1f20303c5b87a4ef556300a531567d
+P 4c43e8b2d2c1d8dcba3cd1c3f2ec4e19ab419430
+R 983c9c689f2d53c2e02840decc5ec993
 U drh
-Z 01e7a916345d0e3901e7a472c5d2f441
+Z ae9009821df61dee832eb776e8a5bada
diff --git a/manifest.uuid b/manifest.uuid
index 2d5de7cdee..1858f041fe 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-4c43e8b2d2c1d8dcba3cd1c3f2ec4e19ab419430
\ No newline at end of file
+b5179baf87aa00ed5cecbdcaa65bee10e112a9e9
\ No newline at end of file
diff --git a/src/select.c b/src/select.c
index 7d9d26602e..a8ea08a781 100644
--- a/src/select.c
+++ b/src/select.c
@@ -900,7 +900,7 @@ static void generateSortTail(
     regRowid = sqlite3GetTempReg(pParse);
   }
   if( p->selFlags & SF_UseSorter ){
-    int regSortOut = sqlite3GetTempReg(pParse);
+    int regSortOut = ++pParse->nMem;
     int ptab2 = pParse->nTab++;
     sqlite3VdbeAddOp3(v, OP_OpenPseudo, ptab2, regSortOut, pOrderBy->nExpr+2);
     addr = 1 + sqlite3VdbeAddOp2(v, OP_SorterSort, iTab, addrBreak);
diff --git a/src/vdbesort.c b/src/vdbesort.c
index 6681aad52d..6ce85811a8 100644
--- a/src/vdbesort.c
+++ b/src/vdbesort.c
@@ -239,15 +239,10 @@ static int vdbeSorterReadVarint(
 ){
   u8 aVarint[9];                  /* Buffer large enough for a varint */
   i64 iOff = *piOffset;           /* Offset in file to read from */
-  int nRead = 9;                  /* Number of bytes to read from file */
   int rc;                         /* Return code */
 
   assert( iEof>iOff );
-  if( (iEof-iOff)<nRead ){
-    nRead = iEof-iOff;
-  }
-
-  rc = sqlite3OsRead(pFile, aVarint, nRead, iOff);
+  rc = sqlite3OsRead(pFile, aVarint, 9, iOff);
   if( rc==SQLITE_OK ){
     *piOffset += getVarint(aVarint, (u64 *)piVal);
   }
@@ -333,7 +328,7 @@ static int vdbeSorterCompare(
     /* This call cannot fail. As the memory is already allocated. */
     r2 = sqlite3VdbeRecordUnpack(pKeyInfo, nKey2, pKey2, aSpace, nSpace);
     assert( r2 && (r2->flags & UNPACKED_NEED_FREE)==0 );
-    assert( r2==aSpace );
+    assert( r2==(UnpackedRecord*)aSpace );
   }else{
     r2 = (UnpackedRecord *)aSpace;
     assert( !bOmitRowid );
@@ -387,10 +382,15 @@ static int vdbeSorterDoCompare(VdbeCursor *pCsr, int iOut){
     iRes = i1;
   }else{
     int res;
-    int rc = vdbeSorterCompare(
+    int rc;
+    assert( pCsr->pSorter->aSpace!=0 );  /* allocated in vdbeSorterMerge() */
+    rc = vdbeSorterCompare(
         pCsr, 0, p1->aKey, p1->nKey, p2->aKey, p2->nKey, &res
     );
-    if( rc!=SQLITE_OK ) return rc;
+    /* The vdbeSorterCompare() call cannot fail since pCsr->pSorter->aSpace
+    ** has already been allocated. */
+    assert( rc==SQLITE_OK );
+
     if( res<=0 ){
       iRes = i1;
     }else{
@@ -606,6 +606,7 @@ static int vdbeSorterListToPMA(sqlite3 *db, VdbeCursor *pCsr){
     i64 iOff = pSorter->iWriteOff;
     SorterRecord *p;
     SorterRecord *pNext = 0;
+    static const char eightZeros[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
 
     pSorter->nPMA++;
     rc = vdbeSorterWriteVarint(pSorter->pTemp1, pSorter->nInMemory, &iOff);
@@ -629,6 +630,11 @@ static int vdbeSorterListToPMA(sqlite3 *db, VdbeCursor *pCsr){
     ));
 
     pSorter->iWriteOff = iOff;
+    if( rc==SQLITE_OK ){
+      /* Terminate each file with 8 extra bytes so that from any offset
+      ** in the file we can always read 9 bytes without a SHORT_READ error */
+      rc = sqlite3OsWrite(pSorter->pTemp1, eightZeros, 8, iOff);
+    }
     pSorter->pRecord = p;
   }
 
-- 
2.47.2