SQLite

        sqlite3_int64 *pi = (isPrefix ? &iLeavesEndBlock : 0);
        rc = fts3SelectLeaf(p, zTerm, nTerm, zRoot, nRoot, &iStartBlock, pi);
        if( rc!=SQLITE_OK ) goto finished;
        if( isPrefix==0 && isScan==0 ) iLeavesEndBlock = iStartBlock;
      }
 
      rc = sqlite3Fts3SegReaderNew(pCsr->nSegment+1, 
          (isPrefix==0 && isScan==0),
          iStartBlock, iLeavesEndBlock, 
          iEndBlock, zRoot, nRoot, &pSeg
      );
      if( rc!=SQLITE_OK ) goto finished;
      rc = fts3SegReaderCursorAppend(pCsr, pSeg);
    }
  }

 finished:

/* fts3_write.c */
int sqlite3Fts3UpdateMethod(sqlite3_vtab*,int,sqlite3_value**,sqlite3_int64*);
int sqlite3Fts3PendingTermsFlush(Fts3Table *);
void sqlite3Fts3PendingTermsClear(Fts3Table *);
int sqlite3Fts3Optimize(Fts3Table *);
int sqlite3Fts3SegReaderNew(int, int, sqlite3_int64,
  sqlite3_int64, sqlite3_int64, const char *, int, Fts3SegReader**);
int sqlite3Fts3SegReaderPending(
  Fts3Table*,int,const char*,int,int,Fts3SegReader**);
void sqlite3Fts3SegReaderFree(Fts3SegReader *);
int sqlite3Fts3AllSegdirs(Fts3Table*, int, int, sqlite3_stmt **);
int sqlite3Fts3ReadLock(Fts3Table *);
int sqlite3Fts3ReadBlock(Fts3Table*, sqlite3_int64, char **, int*, int*);

**
**   fts3SegReaderNext()
**   fts3SegReaderFirstDocid()
**   fts3SegReaderNextDocid()
*/
struct Fts3SegReader {
  int iIdx;                       /* Index within level, or 0x7FFFFFFF for PT */
  int bLookup;                    /* True for a lookup only */

  sqlite3_int64 iStartBlock;      /* Rowid of first leaf block to traverse */
  sqlite3_int64 iLeafEndBlock;    /* Rowid of final leaf block to traverse */
  sqlite3_int64 iEndBlock;        /* Rowid of final block in segment (or 0) */
  sqlite3_int64 iCurrentBlock;    /* Current leaf block (or 0) */

  char *aNode;                    /* Pointer to node data (or NULL) */

  while( pReader->pBlob && rc==SQLITE_OK 
     &&  (pFrom - pReader->aNode + nByte)>pReader->nPopulate
  ){
    rc = fts3SegReaderIncrRead(pReader);
  }
  return rc;
}

/*
** Set an Fts3SegReader cursor to point at EOF.
*/
static void fts3SegReaderSetEof(Fts3SegReader *pSeg){
  if( !fts3SegReaderIsRootOnly(pSeg) ){
    sqlite3_free(pSeg->aNode);
    sqlite3_blob_close(pSeg->pBlob);
    pSeg->pBlob = 0;
  }
  pSeg->aNode = 0;
}

/*
** Move the iterator passed as the first argument to the next term in the
** segment. If successful, SQLITE_OK is returned. If there is no next term,
** SQLITE_DONE. Otherwise, an SQLite error code.
*/
static int fts3SegReaderNext(

        pReader->aNode = pReader->aDoclist = pList->aData;
        pReader->ppNextElem++;
        assert( pReader->aNode );
      }
      return SQLITE_OK;
    }

    fts3SegReaderSetEof(pReader);






    /* If iCurrentBlock>=iLeafEndBlock, this is an EOF condition. All leaf 
    ** blocks have already been traversed.  */
    assert( pReader->iCurrentBlock<=pReader->iLeafEndBlock );
    if( pReader->iCurrentBlock>=pReader->iLeafEndBlock ){
      return SQLITE_OK;
    }

}

/*
** Allocate a new SegReader object.
*/
int sqlite3Fts3SegReaderNew(
  int iAge,                       /* Segment "age". */
  int bLookup,                    /* True for a lookup only */
  sqlite3_int64 iStartLeaf,       /* First leaf to traverse */
  sqlite3_int64 iEndLeaf,         /* Final leaf to traverse */
  sqlite3_int64 iEndBlock,        /* Final block of segment */
  const char *zRoot,              /* Buffer containing root node */
  int nRoot,                      /* Size of buffer containing root node */
  Fts3SegReader **ppReader        /* OUT: Allocated Fts3SegReader */
){

  pReader = (Fts3SegReader *)sqlite3_malloc(sizeof(Fts3SegReader) + nExtra);
  if( !pReader ){
    return SQLITE_NOMEM;
  }
  memset(pReader, 0, sizeof(Fts3SegReader));
  pReader->iIdx = iAge;
  pReader->bLookup = bLookup;
  pReader->iStartBlock = iStartLeaf;
  pReader->iLeafEndBlock = iEndLeaf;
  pReader->iEndBlock = iEndBlock;

  if( nExtra ){
    /* The entire segment is stored in the root node. */
    pReader->aNode = (char *)&pReader[1];

  /* If the Fts3SegFilter defines a specific term (or term prefix) to search 
  ** for, then advance each segment iterator until it points to a term of
  ** equal or greater value than the specified term. This prevents many
  ** unnecessary merge/sort operations for the case where single segment
  ** b-tree leaf nodes contain more than one term.
  */
  for(i=0; pCsr->bRestart==0 && i<pCsr->nSegment; i++){
    int res;
    Fts3SegReader *pSeg = pCsr->apSegment[i];
    do {
      int rc = fts3SegReaderNext(p, pSeg, 0);
      if( rc!=SQLITE_OK ) return rc;
    }while( zTerm && (res = fts3SegReaderTermCmp(pSeg, zTerm, nTerm))<0 );

    if( pSeg->bLookup && res!=0 ){
      fts3SegReaderSetEof(pSeg);
    }
  }
  fts3SegReaderSort(pCsr->apSegment, nSeg, nSeg, fts3SegReaderCmp);

  return SQLITE_OK;
}

int sqlite3Fts3SegReaderStart(

    int nMerge;
    int i;
  
    /* Advance the first pCsr->nAdvance entries in the apSegment[] array
    ** forward. Then sort the list in order of current term again.  
    */
    for(i=0; i<pCsr->nAdvance; i++){
      Fts3SegReader *pSeg = apSegment[i];
      if( pSeg->bLookup ){
        fts3SegReaderSetEof(pSeg);
      }else{
        rc = fts3SegReaderNext(p, pSeg, 0);
      }
      if( rc!=SQLITE_OK ) return rc;
    }
    fts3SegReaderSort(apSegment, nSegment, pCsr->nAdvance, fts3SegReaderCmp);
    pCsr->nAdvance = 0;

    /* If all the seg-readers are at EOF, we're finished. return SQLITE_OK. */
    assert( rc==SQLITE_OK );

#--------------------------------------------------------------------------
# The following test cases - fts3auto-5.* - focus on using prefix indexes.
#
set chunkconfig [fts3_configure_incr_load 1 1]
foreach {tn create pending} {
  1    "fts4(a, b)"                                  1
  2    "fts4(a, b, order=ASC, prefix=1)"             1
  3    "fts4(a, b, order=ASC,  prefix=\"1,3\")"      0
  4    "fts4(a, b, order=DESC, prefix=\"2,4\")"      0
  5    "fts4(a, b, order=DESC, prefix=\"1\")"        0
  6    "fts4(a, b, order=ASC,  prefix=\"1,3\")"      0
} {

  execsql [subst {
    DROP TABLE IF EXISTS t1;
    CREATE VIRTUAL TABLE t1 USING $create;
  }]

# 2012 January 25
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#*************************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this script is testing the FTS3 module.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix fts3prefix2

ifcapable !fts3 {
  finish_test
  return
}

do_execsql_test 1.0 { PRAGMA page_size = 512 }
do_execsql_test 1.1 { 
  CREATE VIRTUAL TABLE t1 USING fts4(x, prefix="2,3");

  BEGIN;
    INSERT INTO t1 VALUES('T TX T TX T TX T TX T TX');
    INSERT INTO t1 SELECT * FROM t1;                       -- 2
    INSERT INTO t1 SELECT * FROM t1;                       -- 4
    INSERT INTO t1 SELECT * FROM t1;                       -- 8
    INSERT INTO t1 SELECT * FROM t1;                       -- 16
    INSERT INTO t1 SELECT * FROM t1;                       -- 32
    INSERT INTO t1 SELECT * FROM t1;                       -- 64
    INSERT INTO t1 SELECT * FROM t1;                       -- 128
    INSERT INTO t1 SELECT * FROM t1;                       -- 256
    INSERT INTO t1 SELECT * FROM t1;                       -- 512
    INSERT INTO t1 SELECT * FROM t1;                       -- 1024
    INSERT INTO t1 SELECT * FROM t1;                       -- 2048
  COMMIT;
}

do_execsql_test 1.2 {
  INSERT INTO t1 SELECT * FROM t1 LIMIT 10;
  INSERT INTO t1 SELECT * FROM t1 LIMIT 10;
  INSERT INTO t1 SELECT * FROM t1 LIMIT 10;
  DELETE FROM t1 WHERE docid > 5;
}

do_execsql_test 1.3 {
  SELECT * FROM t1 WHERE t1 MATCH 'T*';
} {
  {T TX T TX T TX T TX T TX}
  {T TX T TX T TX T TX T TX}
  {T TX T TX T TX T TX T TX}
  {T TX T TX T TX T TX T TX}
  {T TX T TX T TX T TX T TX}
}

finish_test