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Overview
Comment:Reduce memory requirements for ORDER BY combined with LIMIT. Ticket #1586. (CVS 2887)
Downloads: Tarball | ZIP archive | SQL archive
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Files: files | file ages | folders
SHA1:55e703ecac6e03d7364c2d919ba18d7293d6b7f6
User & Date: drh 2006-01-08 05:02:55
Context
2006-01-08
05:26
Remove some cruft from the VDBE. Bring comments up to date. (CVS 2888) check-in: 41aef649 user: drh tags: trunk
05:02
Reduce memory requirements for ORDER BY combined with LIMIT. Ticket #1586. (CVS 2887) check-in: 55e703ec user: drh tags: trunk
2006-01-07
18:48
Invalidate all VDBE cursor row caches in between calls to sqlite3_step() since the emphemeral content that those caches point to might change if the statement is READ UNCOMMITTED. (CVS 2886) check-in: 0ae46131 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/select.c.

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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.286 2006/01/07 13:21:04 danielk1977 Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
  sqliteFree(p);
}

/*
** Insert code into "v" that will push the record on the top of the
** stack into the sorter.
*/
static void pushOntoSorter(Parse *pParse, Vdbe *v, ExprList *pOrderBy){





  sqlite3ExprCodeExprList(pParse, pOrderBy);
  sqlite3VdbeAddOp(v, OP_Sequence, pOrderBy->iECursor, 0);
  sqlite3VdbeAddOp(v, OP_Pull, pOrderBy->nExpr + 1, 0);
  sqlite3VdbeAddOp(v, OP_MakeRecord, pOrderBy->nExpr + 2, 0);
  sqlite3VdbeAddOp(v, OP_IdxInsert, pOrderBy->iECursor, 0);











}

/*
** Add code to implement the OFFSET
*/
static void codeOffset(
  Vdbe *v,          /* Generate code into this VM */
................................................................................

    /* Store the result as data using a unique key.
    */
    case SRT_Table:
    case SRT_VirtualTab: {
      sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
      if( pOrderBy ){
        pushOntoSorter(pParse, v, pOrderBy);
      }else{
        sqlite3VdbeAddOp(v, OP_NewRowid, iParm, 0);
        sqlite3VdbeAddOp(v, OP_Pull, 1, 0);
        sqlite3VdbeAddOp(v, OP_Insert, iParm, 0);
      }
      break;
    }
................................................................................
      sqlite3VdbeAddOp(v, OP_Pop, 1, 0);
      addr2 = sqlite3VdbeAddOp(v, OP_Goto, 0, 0);
      if( pOrderBy ){
        /* At first glance you would think we could optimize out the
        ** ORDER BY in this case since the order of entries in the set
        ** does not matter.  But there might be a LIMIT clause, in which
        ** case the order does matter */
        pushOntoSorter(pParse, v, pOrderBy);
      }else{
        char aff = (iParm>>16)&0xFF;
        aff = sqlite3CompareAffinity(pEList->a[0].pExpr, aff);
        sqlite3VdbeOp3(v, OP_MakeRecord, 1, 0, &aff, 1);
        sqlite3VdbeAddOp(v, OP_IdxInsert, (iParm&0x0000FFFF), 0);
      }
      sqlite3VdbeJumpHere(v, addr2);
................................................................................
    /* If this is a scalar select that is part of an expression, then
    ** store the results in the appropriate memory cell and break out
    ** of the scan loop.
    */
    case SRT_Mem: {
      assert( nColumn==1 );
      if( pOrderBy ){
        pushOntoSorter(pParse, v, pOrderBy);
      }else{
        sqlite3VdbeAddOp(v, OP_MemStore, iParm, 1);
        /* The LIMIT clause will jump out of the loop for us */
      }
      break;
    }
#endif /* #ifndef SQLITE_OMIT_SUBQUERY */
................................................................................
    ** case of a subroutine, the subroutine itself is responsible for
    ** popping the data from the stack.
    */
    case SRT_Subroutine:
    case SRT_Callback: {
      if( pOrderBy ){
        sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
        pushOntoSorter(pParse, v, pOrderBy);
      }else if( eDest==SRT_Subroutine ){
        sqlite3VdbeAddOp(v, OP_Gosub, 0, iParm);
      }else{
        sqlite3VdbeAddOp(v, OP_Callback, nColumn, 0);
      }
      break;
    }
................................................................................
** pLimit and pOffset expressions.  pLimit and pOffset hold the expressions
** that appear in the original SQL statement after the LIMIT and OFFSET
** keywords.  Or NULL if those keywords are omitted. iLimit and iOffset 
** are the integer memory register numbers for counters used to compute 
** the limit and offset.  If there is no limit and/or offset, then 
** iLimit and iOffset are negative.
**
** This routine changes the values if iLimit and iOffset only if
** a limit or offset is defined by pLimit and pOffset.  iLimit and
** iOffset should have been preset to appropriate default values
** (usually but not always -1) prior to calling this routine.
** Only if pLimit!=0 or pOffset!=0 do the limit registers get
** redefined.  The UNION ALL operator uses this property to force
** the reuse of the same limit and offset registers across multiple
** SELECT statements.
................................................................................
  /* 
  ** "LIMIT -1" always shows all rows.  There is some
  ** contraversy about what the correct behavior should be.
  ** The current implementation interprets "LIMIT 0" to mean
  ** no rows.
  */
  if( p->pLimit ){
    int iMem = pParse->nMem++;

    Vdbe *v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pLimit);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_Negative, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iMem, 1);
    VdbeComment((v, "# LIMIT counter"));
    sqlite3VdbeAddOp(v, OP_IfMemZero, iMem, iBreak);
    p->iLimit = iMem;
  }
  if( p->pOffset ){
    int iMem = pParse->nMem++;
    Vdbe *v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pOffset);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_Negative, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iMem, 1);
    VdbeComment((v, "# OFFSET counter"));



    p->iOffset = iMem;
  }





}

/*
** Allocate a virtual index to use for sorting.
*/
static void createSortingIndex(Parse *pParse, Select *p, ExprList *pOrderBy){
  if( pOrderBy ){







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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.287 2006/01/08 05:02:55 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
  sqliteFree(p);
}

/*
** Insert code into "v" that will push the record on the top of the
** stack into the sorter.
*/
static void pushOntoSorter(
  Parse *pParse,         /* Parser context */
  ExprList *pOrderBy,    /* The ORDER BY clause */
  Select *pSelect        /* The whole SELECT statement */
){
  Vdbe *v = pParse->pVdbe;
  sqlite3ExprCodeExprList(pParse, pOrderBy);
  sqlite3VdbeAddOp(v, OP_Sequence, pOrderBy->iECursor, 0);
  sqlite3VdbeAddOp(v, OP_Pull, pOrderBy->nExpr + 1, 0);
  sqlite3VdbeAddOp(v, OP_MakeRecord, pOrderBy->nExpr + 2, 0);
  sqlite3VdbeAddOp(v, OP_IdxInsert, pOrderBy->iECursor, 0);
  if( pSelect->iLimit>=0 ){
    int addr1;
    sqlite3VdbeAddOp(v, OP_MemIncr, pSelect->iLimit+1, 0);
    addr1 = sqlite3VdbeAddOp(v, OP_IfMemPos, pSelect->iLimit+1, 0);
    sqlite3VdbeAddOp(v, OP_Goto, 0, 0);
    sqlite3VdbeJumpHere(v, addr1);
    sqlite3VdbeAddOp(v, OP_Last, pOrderBy->iECursor, 0);
    sqlite3VdbeAddOp(v, OP_Delete, pOrderBy->iECursor, 0);
    sqlite3VdbeJumpHere(v, addr1+1);
    pSelect->iLimit = -1;
  }
}

/*
** Add code to implement the OFFSET
*/
static void codeOffset(
  Vdbe *v,          /* Generate code into this VM */
................................................................................

    /* Store the result as data using a unique key.
    */
    case SRT_Table:
    case SRT_VirtualTab: {
      sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
      if( pOrderBy ){
        pushOntoSorter(pParse, pOrderBy, p);
      }else{
        sqlite3VdbeAddOp(v, OP_NewRowid, iParm, 0);
        sqlite3VdbeAddOp(v, OP_Pull, 1, 0);
        sqlite3VdbeAddOp(v, OP_Insert, iParm, 0);
      }
      break;
    }
................................................................................
      sqlite3VdbeAddOp(v, OP_Pop, 1, 0);
      addr2 = sqlite3VdbeAddOp(v, OP_Goto, 0, 0);
      if( pOrderBy ){
        /* At first glance you would think we could optimize out the
        ** ORDER BY in this case since the order of entries in the set
        ** does not matter.  But there might be a LIMIT clause, in which
        ** case the order does matter */
        pushOntoSorter(pParse, pOrderBy, p);
      }else{
        char aff = (iParm>>16)&0xFF;
        aff = sqlite3CompareAffinity(pEList->a[0].pExpr, aff);
        sqlite3VdbeOp3(v, OP_MakeRecord, 1, 0, &aff, 1);
        sqlite3VdbeAddOp(v, OP_IdxInsert, (iParm&0x0000FFFF), 0);
      }
      sqlite3VdbeJumpHere(v, addr2);
................................................................................
    /* If this is a scalar select that is part of an expression, then
    ** store the results in the appropriate memory cell and break out
    ** of the scan loop.
    */
    case SRT_Mem: {
      assert( nColumn==1 );
      if( pOrderBy ){
        pushOntoSorter(pParse, pOrderBy, p);
      }else{
        sqlite3VdbeAddOp(v, OP_MemStore, iParm, 1);
        /* The LIMIT clause will jump out of the loop for us */
      }
      break;
    }
#endif /* #ifndef SQLITE_OMIT_SUBQUERY */
................................................................................
    ** case of a subroutine, the subroutine itself is responsible for
    ** popping the data from the stack.
    */
    case SRT_Subroutine:
    case SRT_Callback: {
      if( pOrderBy ){
        sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
        pushOntoSorter(pParse, pOrderBy, p);
      }else if( eDest==SRT_Subroutine ){
        sqlite3VdbeAddOp(v, OP_Gosub, 0, iParm);
      }else{
        sqlite3VdbeAddOp(v, OP_Callback, nColumn, 0);
      }
      break;
    }
................................................................................
** pLimit and pOffset expressions.  pLimit and pOffset hold the expressions
** that appear in the original SQL statement after the LIMIT and OFFSET
** keywords.  Or NULL if those keywords are omitted. iLimit and iOffset 
** are the integer memory register numbers for counters used to compute 
** the limit and offset.  If there is no limit and/or offset, then 
** iLimit and iOffset are negative.
**
** This routine changes the values of iLimit and iOffset only if
** a limit or offset is defined by pLimit and pOffset.  iLimit and
** iOffset should have been preset to appropriate default values
** (usually but not always -1) prior to calling this routine.
** Only if pLimit!=0 or pOffset!=0 do the limit registers get
** redefined.  The UNION ALL operator uses this property to force
** the reuse of the same limit and offset registers across multiple
** SELECT statements.
................................................................................
  /* 
  ** "LIMIT -1" always shows all rows.  There is some
  ** contraversy about what the correct behavior should be.
  ** The current implementation interprets "LIMIT 0" to mean
  ** no rows.
  */
  if( p->pLimit ){
    int iMem = pParse->nMem;
    pParse->nMem += 2;
    Vdbe *v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pLimit);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_Negative, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iMem, 0);
    VdbeComment((v, "# LIMIT counter"));
    sqlite3VdbeAddOp(v, OP_IfMemZero, iMem, iBreak);
    p->iLimit = iMem;
  }
  if( p->pOffset ){
    int iMem = pParse->nMem++;
    Vdbe *v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pOffset);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_Negative, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iMem, p->pLimit==0);
    VdbeComment((v, "# OFFSET counter"));
    if( p->pLimit ){
      sqlite3VdbeAddOp(v, OP_Add, 0, 0);
    }
    p->iOffset = iMem;
  }
  if( p->pLimit ){
    Vdbe *v = pParse->pVdbe;
    sqlite3VdbeAddOp(v, OP_MemStore, p->iLimit+1, 1);
    VdbeComment((v, "# LIMIT+OFFSET"));
  }
}

/*
** Allocate a virtual index to use for sorting.
*/
static void createSortingIndex(Parse *pParse, Select *p, ExprList *pOrderBy){
  if( pOrderBy ){