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Improved comments on the OP_Column changes. Optimize out loading of overflow

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pages for content with zero length.  Add test cases for the latter.

FossilOrigin-Name: 0e05679db7aa302a49e087a81f85203844b98cbe
This commit is contained in:
drh
2013-11-20 20:58:00 +00:00
parent c8606e416a
commit 380d685133
4 changed files with 51 additions and 29 deletions
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46
src/vdbe.c
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@@ -2284,11 +2284,11 @@ case OP_Column: {
aType = pC->aType;
aOffset = pC->aOffset;
#ifndef SQLITE_OMIT_VIRTUALTABLE
assert( pC->pVtabCursor==0 );
assert( pC->pVtabCursor==0 ); /* OP_Column never called on virtual table */
#endif
pCrsr = pC->pCursor;
assert( pCrsr!=0 || pC->pseudoTableReg>0 );
assert( pC->pseudoTableReg==0 || pC->nullRow );
assert( pCrsr!=0 || pC->pseudoTableReg>0 ); /* pCrsr NULL on PseudoTables */
assert( pCrsr!=0 || pC->nullRow ); /* pC->nullRow on PseudoTables */
/* If the cursor cache is stale, bring it up-to-date */
rc = sqlite3VdbeCursorMoveto(pC);
@@ -2339,12 +2339,15 @@ case OP_Column: {
goto too_big;
}
}
pC->cacheStatus = p->cacheCtr;
pC->iHdrOffset = getVarint32(pC->aRow, offset);
pC->nHdrParsed = 0;
aOffset[0] = offset;
if( avail<offset ){
/* pC->aRow does not have to hold the entire row, but it does at least
** need to cover the header of the record. If pC->aRow does not contain
** the complete header, then set it to zero, forcing the header to be
** dynamically allocated. */
pC->aRow = 0;
pC->szRow = 0;
}
@@ -2368,8 +2371,8 @@ case OP_Column: {
** parsed and valid information is in aOffset[] and aType[].
*/
if( pC->nHdrParsed<=p2 ){
/* If there is more header available for parsing, try to extract
** additional fields up through the p2-th field
/* If there is more header available for parsing in the record, try
** to extract additional fields up through the p2+1-th field
*/
if( pC->iHdrOffset<aOffset[0] ){
/* Make sure zData points to enough of the record to cover the header. */
@@ -2430,9 +2433,10 @@ case OP_Column: {
}
}
/* If after nHdrParsed is still not up to p2, that means that the record
** has fewer than p2 columns. So the result will be either the default
** value or a NULL. */
/* If after trying to extra new entries from the header, nHdrParsed is
** still not up to p2, that means that the record has fewer than p2
** columns. So the result will be either the default value or a NULL.
*/
if( pC->nHdrParsed<=p2 ){
if( pOp->p4type==P4_MEM ){
sqlite3VdbeMemShallowCopy(pDest, pOp->p4.pMem, MEM_Static);
@@ -2443,33 +2447,33 @@ case OP_Column: {
}
}
/* Get the column information. If aOffset[p2] is non-zero, then
** deserialize the value from the record. If aOffset[p2] is zero,
** then there are not enough fields in the record to satisfy the
** request. In this case, set the value NULL or to P4 if P4 is
** a pointer to a Mem object.
/* Extract the content for the p2+1-th column. Control can only
** reach this point if aOffset[p2], aOffset[p2+1], and aType[p2] are
** all valid.
*/
assert( p2<pC->nHdrParsed );
assert( rc==SQLITE_OK );
if( pC->szRow>=aOffset[p2+1] ){
/* This is the common case where the whole row fits on a single page */
/* This is the common case where the desired content fits on the original
** page - where the content is not on an overflow page */
VdbeMemRelease(pDest);
sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], aType[p2], pDest);
}else{
/* This branch happens only when the row overflows onto multiple pages */
/* This branch happens only when content is on overflow pages */
t = aType[p2];
if( (pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
&& ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0)
if( ((pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
&& ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0))
|| (len = sqlite3VdbeSerialTypeLen(t))==0
){
/* Content is irrelevant for the typeof() function and for
** the length(X) function if X is a blob. So we might as well use
** bogus content rather than reading content from disk. NULL works
** for text and blob and whatever is in the payloadSize64 variable
** will work for everything else. */
zData = t<12 ? (u8*)&payloadSize64 : 0;
** will work for everything else. Content is also irrelevant if
** the content length is 0. */
zData = t<=13 ? (u8*)&payloadSize64 : 0;
sMem.zMalloc = 0;
}else{
len = sqlite3VdbeSerialTypeLen(t);
memset(&sMem, 0, sizeof(sMem));
sqlite3VdbeMemMove(&sMem, pDest);
rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, pC->isIndex,