Use exponential buffer size growth in StrAccum, as long as the size does not

grow to large, to avoid excess memory allocation resize operations.  Also,
document the fact that setting scratch memory causes SQLite to try to avoid
large memory allocations.

FossilOrigin-Name: a518bc3318232d652349eb29303ff250aee40459

manifest

@@ -1,5 +1,5 @@
-C When\senlarging\sthe\ssize\sof\sa\sStrAccum\sobject,\suse\ssqlite3DbMallocSize()\sto\nrecord\sthe\sentire\ssize\sof\sthe\sallocation,\snot\sjust\sthe\srequested\ssize.
+C Use\sexponential\sbuffer\ssize\sgrowth\sin\sStrAccum,\sas\slong\sas\sthe\ssize\sdoes\snot\ngrow\sto\slarge,\sto\savoid\sexcess\smemory\sallocation\sresize\soperations.\s\sAlso,\ndocument\sthe\sfact\sthat\ssetting\sscratch\smemory\scauses\sSQLite\sto\stry\sto\savoid\nlarge\smemory\sallocations.
-D 2014-11-03T13:24:12.668
+D 2014-11-03T14:46:29.027
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in cf57f673d77606ab0f2d9627ca52a9ba1464146a
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -223,13 +223,13 @@ F src/pcache.h 9b559127b83f84ff76d735c8262f04853be0c59a
 F src/pcache1.c e412cb585f777c840ddce0500eddc5c6043c2bb5
 F src/pragma.c 3f3e959390a10c0131676f0e307acce372777e0f
 F src/prepare.c b7b7bf020bd4c962f7c8aed5a3c542c7dfe9f9c7
-F src/printf.c ee13daccd49ddf767d057bc98395c9e83d4e2067
+F src/printf.c 9e75a6a0b55bf61cfff7d7e19d89834a1b938236
 F src/random.c ba2679f80ec82c4190062d756f22d0c358180696
 F src/resolve.c 4965007d6497b6a4d7a6d98751cc39712885f952
 F src/rowset.c eccf6af6d620aaa4579bd3b72c1b6395d9e9fa1e
 F src/select.c 428165951748151e87a15295b7357221433e311b
 F src/shell.c 282f8f5278e0c78eb442217531172ec9e1538796
-F src/sqlite.h.in c3c6180be49d91d3b0001a8d3c604684f361adc2
+F src/sqlite.h.in dd0cb63fb7cb558892afe8253c3279c508c50329
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h 17d487c3c91b0b8c584a32fbeb393f6f795eea7d
 F src/sqliteInt.h 8f67ca79e957b8ece7453b8e320b6a996e1b4761
@@ -296,7 +296,7 @@ F src/vdbeapi.c 02d8afcff710eb35e3d9e49cb677308296b00009
 F src/vdbeaux.c 3d6b2b412ef2193aa4729922dfc5df1efadbf6df
 F src/vdbeblob.c 8b5442ff0954c44b45cbabbe2e94091a2e16fdef
 F src/vdbemem.c 31d8eabb0cd78bfeab4e5124c7363c3e9e54db9f
-F src/vdbesort.c 975aeffa99acb0991b2f288d30294756bff41438
+F src/vdbesort.c daf87ea542df088ac4607660d09976d36b6bd95d
 F src/vdbetrace.c 7e4222955e07dd707a2f360c0eb73452be1cb010
 F src/vtab.c 2a30791bbd7926b589401bd09c3abb33de563793
 F src/wal.c 10e7de7ce90865a68153f001a61f1d985cd17983
@@ -1210,7 +1210,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 49188b2bb53a92b0b0b6aaf8247edeb0c1bcd1f5
+P 3dda3c937469ce661d1cd0e8d8963a03e698ee39
-R 041ffec3947ff9e90700478ea54978f5
+R e2c699e9cb6d832117ea76de0a03f26b
 U drh
-Z 42c888343c3ca87538d56b9b17ae76ab
+Z 91c9a2887aef0ce4f97740bae4c1a9ba

manifest.uuid

@@ -1 +1 @@
-3dda3c937469ce661d1cd0e8d8963a03e698ee39
+a518bc3318232d652349eb29303ff250aee40459

src/printf.c

@@ -770,6 +770,11 @@ static int sqlite3StrAccumEnlarge(StrAccum *p, int N){
     char *zOld = (p->zText==p->zBase ? 0 : p->zText);
     i64 szNew = p->nChar;
     szNew += N + 1;
+    if( szNew+p->nChar<=p->mxAlloc ){
+      /* Force exponential buffer size growth as long as it does not overflow,
+      ** to avoid having to call this routine too often */
+      szNew += p->nChar;
+    }
     if( szNew > p->mxAlloc ){
       sqlite3StrAccumReset(p);
       setStrAccumError(p, STRACCUM_TOOBIG);

src/sqlite.h.in

@@ -1535,8 +1535,7 @@ struct sqlite3_mem_methods {
 ** scratch memory.  ^(There are three arguments:  A pointer an 8-byte
 ** aligned memory buffer from which the scratch allocations will be
 ** drawn, the size of each scratch allocation (sz),
-** and the maximum number of scratch allocations (N).)^  The sz
+** and the maximum number of scratch allocations (N).)^
-** argument must be a multiple of 16.
 ** The first argument must be a pointer to an 8-byte aligned buffer
 ** of at least sz*N bytes of memory.
 ** ^SQLite will not use more than two scratch buffers per thread and not
@@ -1548,7 +1547,13 @@ struct sqlite3_mem_methods {
 ** of the size of the WAL file.
 ** ^If SQLite needs needs additional
 ** scratch memory beyond what is provided by this configuration option, then 
-** [sqlite3_malloc()] will be used to obtain the memory needed.</dd>
+** [sqlite3_malloc()] will be used to obtain the memory needed.<p>
+** ^When the application provides any amount of scratch memory using
+** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
+** [sqlite3_malloc|heap allocations].
+** This can help [Robson proof|prevent memory allocation failures] due to heap
+** fragmentation in low-memory embedded systems.
+** </dd>
 **
 ** [[SQLITE_CONFIG_PAGECACHE]] <dt>SQLITE_CONFIG_PAGECACHE</dt>
 ** <dd> ^This option specifies a static memory buffer that SQLite can use for

src/vdbesort.c

@@ -847,11 +847,9 @@ int sqlite3VdbeSorterInit(
       if( mxCache<SORTER_MIN_WORKING ) mxCache = SORTER_MIN_WORKING;
       pSorter->mxPmaSize = mxCache * pgsz;
 
-      /* If the application has not configure scratch memory using
+      /* EVIDENCE-OF: R-26747-61719 When the application provides any amount of
-      ** SQLITE_CONFIG_SCRATCH then we assume it is OK to do large memory
+      ** scratch memory using SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary
-      ** allocations.  If scratch memory has been configured, then assume
+      ** large heap allocations.
-      ** large memory allocations should be avoided to prevent heap
-      ** fragmentation.
       */
       if( sqlite3GlobalConfig.pScratch==0 ){
         assert( pSorter->iMemory==0 );