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Modify the OP_RowData opcode so that when P3!=0 it is allowed to hold an

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ephemeral copy of the content.  This avoids unnecessary memcpy() operations
in the xfer-optimization and VACUUM.

FossilOrigin-Name: 6e106acd74da3baa5c308a76443d2f0a7c904e5e
This commit is contained in:
drh
2017-01-09 15:44:25 +00:00
parent f4e994b23a
commit e7b554d615
4 changed files with 27 additions and 20 deletions
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27
src/vdbe.c
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@@ -4632,7 +4632,7 @@ case OP_SorterData: {
break;
}
/* Opcode: RowData P1 P2 * * *
/* Opcode: RowData P1 P2 P3 * *
** Synopsis: r[P2]=data
**
** Write into register P2 the complete row content for the row at
@@ -4646,14 +4646,26 @@ case OP_SorterData: {
**
** If the P1 cursor must be pointing to a valid row (not a NULL row)
** of a real table, not a pseudo-table.
**
** If P3!=0 then this opcode is allowed to make an ephermeral pointer
** into the database page. That means that the content of the output
** register will be invalidated as soon as the cursor moves - including
** moves caused by other cursors that "save" the the current cursors
** position in order that they can write to the same table. If P3==0
** then a copy of the data is made into memory. P3!=0 is faster, but
** P3==0 is safer.
**
** If P3!=0 then the content of the P2 register is unsuitable for use
** in OP_Result and any OP_Result will invalidate the P2 register content.
** The P2 register content is invalided by opcodes like OP_Function or
** by any use of another cursor pointing to the same table.
*/
case OP_RowData: {
VdbeCursor *pC;
BtCursor *pCrsr;
u32 n;
pOut = &aMem[pOp->p2];
memAboutToChange(p, pOut);
pOut = out2Prerelease(p, pOp);
assert( pOp->p1>=0 && pOp->p1<p->nCursor );
pC = p->apCsr[pOp->p1];
@@ -4684,14 +4696,9 @@ case OP_RowData: {
goto too_big;
}
testcase( n==0 );
if( sqlite3VdbeMemClearAndResize(pOut, MAX(n,32)) ){
goto no_mem;
}
pOut->n = n;
MemSetTypeFlag(pOut, MEM_Blob);
rc = sqlite3BtreePayload(pCrsr, 0, n, pOut->z);
rc = sqlite3VdbeMemFromBtree(pCrsr, 0, n, pOut);
if( rc ) goto abort_due_to_error;
pOut->enc = SQLITE_UTF8; /* In case the blob is ever cast to text */
if( !pOp->p3 ) Deephemeralize(pOut);
UPDATE_MAX_BLOBSIZE(pOut);
REGISTER_TRACE(pOp->p2, pOut);
break;