SQLite

  /* TODO(shess) Explore whether partially flushing the buffer on
  ** forced-flush would provide better performance.  I suspect that if
  ** we ordered the doclists by size and flushed the largest until the
  ** buffer was half empty, that would let the less frequent terms
  ** generate longer doclists.
  */
  if( iDocid<p->iPrevDocid 
   || (iDocid==p->iPrevDocid && p->bPrevDelete==0)
   || p->iPrevLangid!=iLangid
   || p->nPendingData>p->nMaxPendingData 
  ){
    int rc = sqlite3Fts3PendingTermsFlush(p);
    if( rc!=SQLITE_OK ) return rc;
  }
  p->iPrevDocid = iDocid;

  /* Begin generating code. */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ) goto update_cleanup;
  if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);
  sqlite3BeginWriteOperation(pParse, 1, iDb);












  /* Allocate required registers. */
  if( !IsVirtual(pTab) ){
    regRowSet = ++pParse->nMem;
    regOldRowid = regNewRowid = ++pParse->nMem;
    if( chngPk || pTrigger || hasFK ){
      regOld = pParse->nMem + 1;
      pParse->nMem += pTab->nCol;
    }
    if( chngKey || pTrigger || hasFK ){
      regNewRowid = ++pParse->nMem;
    }
    regNew = pParse->nMem + 1;
    pParse->nMem += pTab->nCol;
  }

  /* Start the view context. */
  if( isView ){
    sqlite3AuthContextPush(pParse, &sContext, pTab->zName);
  }

  /* If we are trying to update a view, realize that view into

  /* Resolve the column names in all the expressions in the
  ** WHERE clause.
  */
  if( sqlite3ResolveExprNames(&sNC, pWhere) ){
    goto update_cleanup;
  }

#ifndef SQLITE_OMIT_VIRTUALTABLE
  /* Virtual tables must be handled separately */
  if( IsVirtual(pTab) ){
    updateVirtualTable(pParse, pTabList, pTab, pChanges, pRowidExpr, aXRef,
                       pWhere, onError);
    goto update_cleanup;
  }
#endif

  /* Begin the database scan
  */
  if( HasRowid(pTab) ){
    sqlite3VdbeAddOp3(v, OP_Null, 0, regRowSet, regOldRowid);
    pWInfo = sqlite3WhereBegin(
        pParse, pTabList, pWhere, 0, 0, WHERE_ONEPASS_DESIRED, iIdxCur

 #undef pTrigger
#endif

#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** Generate code for an UPDATE of a virtual table.
**
** There are two possible strategies - the default and the special 
** "onepass" strategy. Onepass is only used if the virtual table 
** implementation indicates that pWhere may match at most one row.
**
** The default strategy is to create an ephemeral table that contains
** for each row to be changed:
**
**   (A)  The original rowid of that row.
**   (B)  The revised rowid for the row.
**   (C)  The content of every column in the row.
**
** Then loop through the contents of this ephemeral table executing a


** VUpdate for each row. When finished, drop the ephemeral table.
**
** The "onepass" strategy does not use an ephemeral table. Instead, it
** stores the same values (A, B and C above) in a register array and

** makes a single invocation of VUpdate.
*/
static void updateVirtualTable(
  Parse *pParse,       /* The parsing context */
  SrcList *pSrc,       /* The virtual table to be modified */
  Table *pTab,         /* The virtual table */
  ExprList *pChanges,  /* The columns to change in the UPDATE statement */
  Expr *pRowid,        /* Expression used to recompute the rowid */
  int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */
  Expr *pWhere,        /* WHERE clause of the UPDATE statement */
  int onError          /* ON CONFLICT strategy */
){
  Vdbe *v = pParse->pVdbe;  /* Virtual machine under construction */



  int ephemTab;             /* Table holding the result of the SELECT */
  int i;                    /* Loop counter */


  sqlite3 *db = pParse->db; /* Database connection */
  const char *pVTab = (const char*)sqlite3GetVTable(db, pTab);

  WhereInfo *pWInfo;

  int nArg = 2 + pTab->nCol;      /* Number of arguments to VUpdate */
  int regArg;                     /* First register in VUpdate arg array */


  int regRec;                     /* Register in which to assemble record */
  int regRowid;                   /* Register for ephem table rowid */

  int iCsr = pSrc->a[0].iCursor;  /* Cursor used for virtual table scan */
  int aDummy[2];                  /* Unused arg for sqlite3WhereOkOnePass() */






  int bOnePass;                   /* True to use onepass strategy */
  int addr;                       /* Address of OP_OpenEphemeral */
  NameContext sNC;




  /* Allocate nArg registers to martial the arguments to VUpdate. Then
  ** create and open the ephemeral table in which the records created from
  ** these arguments will be temporarily stored. */

  assert( v );
  ephemTab = pParse->nTab++;
  addr= sqlite3VdbeAddOp2(v, OP_OpenEphemeral, ephemTab, nArg);
  regArg = pParse->nMem + 1;
  pParse->nMem += nArg;
  regRec = ++pParse->nMem;
  regRowid = ++pParse->nMem;

  /* Start scanning the virtual table */
  pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0,0,WHERE_ONEPASS_DESIRED,0);
  if( pWInfo==0 ) return;

  /* Populate the argument registers. */
  sqlite3VdbeAddOp2(v, OP_Rowid, iCsr, regArg);
  if( pRowid ){
    sqlite3ExprCode(pParse, pRowid, regArg+1);
  }else{
    sqlite3VdbeAddOp2(v, OP_Rowid, iCsr, regArg+1);
  }
  for(i=0; i<pTab->nCol; i++){
    if( aXRef[i]>=0 ){
      sqlite3ExprCode(pParse, pChanges->a[aXRef[i]].pExpr, regArg+2+i);
    }else{
      sqlite3VdbeAddOp3(v, OP_VColumn, iCsr, i, regArg+2+i);
    }
  }

  bOnePass = sqlite3WhereOkOnePass(pWInfo, aDummy);

  if( bOnePass ){
    /* If using the onepass strategy, no-op out the OP_OpenEphemeral coded
    ** above. Also, if this is a top-level parse (not a trigger), clear the
    ** multi-write flag so that the VM does not open a statement journal */
    sqlite3VdbeChangeToNoop(v, addr);
    if( sqlite3ParseToplevel(pParse)==pParse ){
      pParse->isMultiWrite = 0;
    }
  }else{
    /* Create a record from the argument register contents and insert it into
    ** the ephemeral table. */
    sqlite3VdbeAddOp3(v, OP_MakeRecord, regArg, nArg, regRec);
    sqlite3VdbeAddOp2(v, OP_NewRowid, ephemTab, regRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, ephemTab, regRec, regRowid);
  }

  /* End the virtual table scan */
  sqlite3WhereEnd(pWInfo);

  if( bOnePass==0 ){
    /* Begin scannning through the ephemeral table. */
    addr = sqlite3VdbeAddOp2(v, OP_Rewind, ephemTab, 0); VdbeCoverage(v);


    /* Extract arguments from the current row of the ephemeral table and 
    ** invoke the VUpdate method.  */
    for(i=0; i<nArg; i++){
      sqlite3VdbeAddOp3(v, OP_Column, ephemTab, i, regArg+i);
    }
  }
  sqlite3VtabMakeWritable(pParse, pTab);
  sqlite3VdbeAddOp4(v, OP_VUpdate, 0, nArg, regArg, pVTab, P4_VTAB);
  sqlite3VdbeChangeP5(v, onError==OE_Default ? OE_Abort : onError);
  sqlite3MayAbort(pParse);

  /* End of the ephemeral table scan */
  if( bOnePass==0 ){
    sqlite3VdbeAddOp2(v, OP_Next, ephemTab, addr+1); VdbeCoverage(v);
    sqlite3VdbeJumpHere(v, addr);
    sqlite3VdbeAddOp2(v, OP_Close, ephemTab, 0);
  }


}
#endif /* SQLITE_OMIT_VIRTUALTABLE */

  6    "INSERT OR ROLLBACK $T2"   1 1 {{a b c d} {e f g h}}
  7    "INSERT OR ABORT    $T2"   1 1 {{a b c d} {e f g h} {i j k l}}
  8    "INSERT OR FAIL     $T2"   1 1 {{a b c d} {e f g h} {i j k l} z}
  9    "INSERT OR IGNORE   $T2"   1 0 {{a b c d} {e f g h} {i j k l} z}
  10   "INSERT OR REPLACE  $T2"   1 0 {{a b c d} y {i j k l} z}

  11   "UPDATE OR ROLLBACK $T3"   0 1 {{a b c d} {e f g h}}
  12   "UPDATE OR ABORT    $T3"   0 1 {{a b c d} {e f g h} {i j k l}}
  13   "UPDATE OR FAIL     $T3"   0 1 {{a b c d} {e f g h} {i j k l}}
  14   "UPDATE OR IGNORE   $T3"   0 0 {{a b c d} {e f g h} {i j k l}}
  15   "UPDATE OR REPLACE  $T3"   0 0 {{a b c d} {i j k l}}

  16   "UPDATE OR ROLLBACK $T4"   1 1 {{a b c d} {e f g h}}
  17   "UPDATE OR ABORT    $T4"   1 1 {{a b c d} {e f g h} {i j k l}}
  18   "UPDATE OR FAIL     $T4"   1 1 {{e f g h} {i j k l} {a b c d}}
  19   "UPDATE OR IGNORE   $T4"   1 0 {{e f g h} {i j k l} {a b c d}}
  20   "UPDATE OR REPLACE  $T4"   1 0 {{e f g h} {a b c d}}
}] {

} {0}
do_test 3.1.3 {
  db transaction { 
    insert_doc 1 2 3 4 5 6 7 8 9
    delete_doc 9 8 7
  }
  execsql { SELECT level, idx, second(end_block) FROM x3_segdir }
} {0 0 591 0 1 65 0 2 72 0 3 76}
do_test 3.1.4 {
  execsql { INSERT INTO x3(x3) VALUES('optimize') }
  execsql { SELECT level, idx, second(end_block) FROM x3_segdir }
} {0 0 412}

do_test 3.2.1 {
  execsql { DELETE FROM x3 }
  insert_doc 8 7 6 5 4 3 2 1
  delete_doc 7 8
  execsql { SELECT count(*) FROM x3_segdir }
} {10}