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Improved comments on the cell-overwrite optimization code.

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FossilOrigin-Name: a4fe966da2fc479b18bf521ff596000410af3a611f7d8723d126795e595ccf22
This commit is contained in:
drh
2018-05-07 17:27:04 +00:00
parent e3c05a5597
commit d720d394d0
3 changed files with 57 additions and 31 deletions
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73
src/btree.c
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@@ -8332,43 +8332,70 @@ int sqlite3BtreeInsert(
invalidateIncrblobCursors(p, pCur->pgnoRoot, pX->nKey, 0);
/* If BTREE_SAVEPOSITION is set, the cursor must already be pointing
** to a row with the same key as the new entry being inserted. */
assert( (flags & BTREE_SAVEPOSITION)==0 ||
((pCur->curFlags&BTCF_ValidNKey)!=0 && pX->nKey==pCur->info.nKey) );
** to a row with the same key as the new entry being inserted.
*/
#ifdef SQLITE_DEBUG
if( flags & BTREE_SAVEPOSITION ){
assert( pCur->curFlags & BTCF_ValidNKey );
assert( pX->nKey==pCur->info.nKey );
assert( pCur->info.nSize!=0 );
assert( loc==0 );
}
#endif
/* If the cursor is currently on the last row and we are appending a
** new row onto the end, set the "loc" to avoid an unnecessary
** btreeMoveto() call */
/* On the other hand, BTREE_SAVEPOSITION==0 does not imply
** that the cursor is not pointing to a row to be overwritten.
** So do a complete check.
*/
if( (pCur->curFlags&BTCF_ValidNKey)!=0 && pX->nKey==pCur->info.nKey ){
/* The current is currently pointing to the entry that is to be
/* The cursor is pointing to the entry that is to be
** overwritten */
assert( pX->nData>=0 && pX->nZero>=0 );
if( pCur->info.nSize!=0
&& pCur->info.nPayload==(u32)pX->nData+pX->nZero
){
/* New entry is the same size as the old. Do an overwrite */
return btreeOverwriteCell(pCur, pX);
}
loc = 0;
assert( loc==0 );
}else if( loc==0 ){
/* The cursor is *not* pointing to the cell to be overwritten, nor
** to an adjacent cell. Move the cursor so that it is pointing either
** to the cell to be overwritten or an adjacent cell.
*/
rc = sqlite3BtreeMovetoUnpacked(pCur, 0, pX->nKey, flags!=0, &loc);
if( rc ) return rc;
}
}else if( loc==0 && (flags & BTREE_SAVEPOSITION)==0 ){
if( pX->nMem ){
UnpackedRecord r;
r.pKeyInfo = pCur->pKeyInfo;
r.aMem = pX->aMem;
r.nField = pX->nMem;
r.default_rc = 0;
r.errCode = 0;
r.r1 = 0;
r.r2 = 0;
r.eqSeen = 0;
rc = sqlite3BtreeMovetoUnpacked(pCur, &r, 0, flags!=0, &loc);
}else{
rc = btreeMoveto(pCur, pX->pKey, pX->nKey, flags!=0, &loc);
}else{
/* This is an index or a WITHOUT ROWID table */
/* If BTREE_SAVEPOSITION is set, the cursor must already be pointing
** to a row with the same key as the new entry being inserted.
*/
assert( (flags & BTREE_SAVEPOSITION)==0 || loc==0 );
/* If the cursor is not already pointing either to the cell to be
** overwritten, or if a new cell is being inserted, if the cursor is
** not pointing to an immediately adjacent cell, then move the cursor
** so that it does.
*/
if( loc==0 && (flags & BTREE_SAVEPOSITION)==0 ){
if( pX->nMem ){
UnpackedRecord r;
r.pKeyInfo = pCur->pKeyInfo;
r.aMem = pX->aMem;
r.nField = pX->nMem;
r.default_rc = 0;
r.errCode = 0;
r.r1 = 0;
r.r2 = 0;
r.eqSeen = 0;
rc = sqlite3BtreeMovetoUnpacked(pCur, &r, 0, flags!=0, &loc);
}else{
rc = btreeMoveto(pCur, pX->pKey, pX->nKey, flags!=0, &loc);
}
if( rc ) return rc;
}
if( rc ) return rc;
}
assert( pCur->eState==CURSOR_VALID || (pCur->eState==CURSOR_INVALID && loc) );