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

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

FossilOrigin-Name: 6e106acd74da3baa5c308a76443d2f0a7c904e5e

2 files changed, 19 insertions, 12 deletions

diff --git a/src/insert.c b/src/insert.c
index e55ea2d9f..a33ee1235 100644
--- a/src/insert.c
+++ b/src/insert.c
@@ -2138,7 +2138,7 @@ static int xferOptimization(
       addr1 = sqlite3VdbeAddOp2(v, OP_Rowid, iSrc, regRowid);
       assert( (pDest->tabFlags & TF_Autoincrement)==0 );
     }
-    sqlite3VdbeAddOp2(v, OP_RowData, iSrc, regData);
+    sqlite3VdbeAddOp3(v, OP_RowData, iSrc, regData, 1);
     if( db->flags & SQLITE_Vacuum ){
       sqlite3VdbeAddOp3(v, OP_Last, iDest, 0, -1);
       insFlags = OPFLAG_NCHANGE|OPFLAG_LASTROWID|
@@ -2170,7 +2170,7 @@ static int xferOptimization(
     sqlite3VdbeChangeP5(v, OPFLAG_BULKCSR);
     VdbeComment((v, "%s", pDestIdx->zName));
     addr1 = sqlite3VdbeAddOp2(v, OP_Rewind, iSrc, 0); VdbeCoverage(v);
-    sqlite3VdbeAddOp2(v, OP_RowData, iSrc, regData);
+    sqlite3VdbeAddOp3(v, OP_RowData, iSrc, regData, 1);
     if( db->flags & SQLITE_Vacuum ){
       /* This INSERT command is part of a VACUUM operation, which guarantees
       ** that the destination table is empty. If all indexed columns use
diff --git a/src/vdbe.c b/src/vdbe.c
index 5e707a623..698092eb5 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -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;