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Optimize calls to sqlite3_mprintf("%z...") so that they attempt to append

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text onto the end of the existing memory allocation rather than reallocating
and copying.

FossilOrigin-Name: 4bc8a48e644562f6e6192f4c6fc4a70f6bb59f8126ed6c6dc876bedf65d74cda
This commit is contained in:
drh
2018-02-20 15:23:37 +00:00
parent b0b6f8783c
commit cc398969e0
6 changed files with 30 additions and 11 deletions
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17
src/printf.c
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@@ -206,6 +206,11 @@ void sqlite3VXPrintf(
PrintfArguments *pArgList = 0; /* Arguments for SQLITE_PRINTF_SQLFUNC */
char buf[etBUFSIZE]; /* Conversion buffer */
/* pAccum never starts out with an empty buffer that was obtained from
** malloc(). This precondition is required by the mprintf("%z...")
** optimization. */
assert( pAccum->nChar>0 || (pAccum->printfFlags&SQLITE_PRINTF_MALLOCED)==0 );
bufpt = 0;
if( (pAccum->printfFlags & SQLITE_PRINTF_SQLFUNC)!=0 ){
pArgList = va_arg(ap, PrintfArguments*);
@@ -681,6 +686,18 @@ void sqlite3VXPrintf(
if( bufpt==0 ){
bufpt = "";
}else if( xtype==etDYNSTRING ){
if( pAccum->nChar==0 && pAccum->mxAlloc && width==0 && precision<0 ){
/* Special optimization for sqlite3_mprintf("%z..."):
** Extend an existing memory allocation rather than creating
** a new one. */
assert( (pAccum->printfFlags&SQLITE_PRINTF_MALLOCED)==0 );
pAccum->zText = bufpt;
pAccum->nAlloc = sqlite3DbMallocSize(pAccum->db, bufpt);
pAccum->nChar = 0x7fffffff & (int)strlen(bufpt);
pAccum->printfFlags |= SQLITE_PRINTF_MALLOCED;
length = 0;
break;
}
zExtra = bufpt;
}
if( precision>=0 ){