Segment lhs;                    /* Left-hand (main) segment */
  int nRight;                     /* Size of apRight[] array */
  Segment *aRhs;                  /* Old segments being merged into this */
  int iSplitTopic;                /* Split key topic (if nRight>0) */
  void *pSplitKey;                /* Pointer to split-key (if nRight>0) */
  int nSplitKey;                  /* Number of bytes in split-key */

  int iAge;                       /* Number of times data has been written */

  Merge *pMerge;                  /* Merge operation currently underway */
  Level *pNext;                   /* Next level in tree */
};















/*
** A structure describing an ongoing merge. There is an instance of this
** structure for every Level currently undergoing a merge in the worker
** snapshot.
**
** It is assumed that code that uses an instance of this structure has

  Segment lhs;                    /* Left-hand (main) segment */
  int nRight;                     /* Size of apRight[] array */
  Segment *aRhs;                  /* Old segments being merged into this */
  int iSplitTopic;                /* Split key topic (if nRight>0) */
  void *pSplitKey;                /* Pointer to split-key (if nRight>0) */
  int nSplitKey;                  /* Number of bytes in split-key */

  u16 iAge;                       /* Number of times data has been written */
  u16 flags;                      /* Mask of LEVEL_XXX bits */
  Merge *pMerge;                  /* Merge operation currently underway */
  Level *pNext;                   /* Next level in tree */
};

/*
** The Level.flags field is set to a combination of the following bits.
**
** LEVEL_FREELIST_ONLY:
**   Set if the level consists entirely of free-list entries. 
**
** LEVEL_INCOMPLETE:
**   This is set while a new toplevel level is being constructed. It is
**   never set for any level other than a new toplevel.
*/
#define LEVEL_FREELIST_ONLY      0x0001
#define LEVEL_INCOMPLETE         0x0002


/*
** A structure describing an ongoing merge. There is an instance of this
** structure for every Level currently undergoing a merge in the worker
** snapshot.
**
** It is assumed that code that uses an instance of this structure has

**
**   Append points:
**
**     8 integers (4 * 64-bit page numbers). See ckptExportAppendlist().
**
**   For each level in the database, a level record. Formatted as follows:
**
**     0. Age of the level.

**     1. The number of right-hand segments (nRight, possibly 0),
**     2. Segment record for left-hand segment (8 integers defined below),
**     3. Segment record for each right-hand segment (8 integers defined below),
**     4. If nRight>0, The number of segments involved in the merge
**     5. if nRight>0, Current nSkip value (see Merge structure defn.),
**     6. For each segment in the merge:
**        5a. Page number of next cell to read during merge (this field
................................................................................
  int *piOut,                     /* IN/OUT: Size of checkpoint so far */
  int *pRc                        /* IN/OUT: Error code */
){
  int iOut = *piOut;
  Merge *pMerge;

  pMerge = pLevel->pMerge;
  ckptSetValue(p, iOut++, pLevel->iAge, pRc);
  ckptSetValue(p, iOut++, pLevel->nRight, pRc);
  ckptExportSegment(&pLevel->lhs, p, &iOut, pRc);

  assert( (pLevel->nRight>0)==(pMerge!=0) );
  if( pMerge ){
    int i;
    for(i=0; i<pLevel->nRight; i++){
................................................................................
  for(i=0; rc==LSM_OK && i<nLevel; i++){
    int iRight;
    Level *pLevel;

    /* Allocate space for the Level structure and Level.apRight[] array */
    pLevel = (Level *)lsmMallocZeroRc(pDb->pEnv, sizeof(Level), &rc);
    if( rc==LSM_OK ){
      pLevel->iAge = aIn[iIn++];


      pLevel->nRight = aIn[iIn++];
      if( pLevel->nRight ){
        int nByte = sizeof(Segment) * pLevel->nRight;
        pLevel->aRhs = (Segment *)lsmMallocZeroRc(pDb->pEnv, nByte, &rc);
      }
      if( rc==LSM_OK ){
        *ppNext = pLevel;

**
**   Append points:
**
**     8 integers (4 * 64-bit page numbers). See ckptExportAppendlist().
**
**   For each level in the database, a level record. Formatted as follows:
**
**     0. Age of the level (least significant 16-bits). And flags mask (most
**        significant 16-bits).
**     1. The number of right-hand segments (nRight, possibly 0),
**     2. Segment record for left-hand segment (8 integers defined below),
**     3. Segment record for each right-hand segment (8 integers defined below),
**     4. If nRight>0, The number of segments involved in the merge
**     5. if nRight>0, Current nSkip value (see Merge structure defn.),
**     6. For each segment in the merge:
**        5a. Page number of next cell to read during merge (this field
................................................................................
  int *piOut,                     /* IN/OUT: Size of checkpoint so far */
  int *pRc                        /* IN/OUT: Error code */
){
  int iOut = *piOut;
  Merge *pMerge;

  pMerge = pLevel->pMerge;
  ckptSetValue(p, iOut++, (u32)pLevel->iAge + (u32)(pLevel->flags<<16), pRc);
  ckptSetValue(p, iOut++, pLevel->nRight, pRc);
  ckptExportSegment(&pLevel->lhs, p, &iOut, pRc);

  assert( (pLevel->nRight>0)==(pMerge!=0) );
  if( pMerge ){
    int i;
    for(i=0; i<pLevel->nRight; i++){
................................................................................
  for(i=0; rc==LSM_OK && i<nLevel; i++){
    int iRight;
    Level *pLevel;

    /* Allocate space for the Level structure and Level.apRight[] array */
    pLevel = (Level *)lsmMallocZeroRc(pDb->pEnv, sizeof(Level), &rc);
    if( rc==LSM_OK ){
      pLevel->iAge = (u16)(aIn[iIn] & 0x0000FFFF);
      pLevel->flags = (u16)((aIn[iIn]>>16) & 0x0000FFFF);
      iIn++;
      pLevel->nRight = aIn[iIn++];
      if( pLevel->nRight ){
        int nByte = sizeof(Segment) * pLevel->nRight;
        pLevel->aRhs = (Segment *)lsmMallocZeroRc(pDb->pEnv, nByte, &rc);
      }
      if( rc==LSM_OK ){
        *ppNext = pLevel;

static int multiCursorAddAll(MultiCursor *pCsr, Snapshot *pSnap){
  Level *pLvl;
  int nPtr = 0;
  int iPtr = 0;
  int rc = LSM_OK;

  for(pLvl=pSnap->pLevel; pLvl; pLvl=pLvl->pNext){
    if( pLvl->iAge<0 ) continue;





    nPtr += (1 + pLvl->nRight);
  }

  assert( pCsr->aPtr==0 );
  pCsr->aPtr = lsmMallocZeroRc(pCsr->pDb->pEnv, sizeof(SegmentPtr) * nPtr, &rc);
  if( rc==LSM_OK ) pCsr->nPtr = nPtr;

  for(pLvl=pSnap->pLevel; pLvl && rc==LSM_OK; pLvl=pLvl->pNext){
    int i;
    if( pLvl->iAge<0 ) continue;
    pCsr->aPtr[iPtr].pLevel = pLvl;
    pCsr->aPtr[iPtr].pSeg = &pLvl->lhs;
    iPtr++;
    for(i=0; i<pLvl->nRight; i++){
      pCsr->aPtr[iPtr].pLevel = pLvl;
      pCsr->aPtr[iPtr].pSeg = &pLvl->aRhs[i];
      iPtr++;
................................................................................
  if( pCsr ){
    pCsr->pDb = pDb;
    rc = multiCursorVisitFreelist(pCsr);
    if( rc==LSM_OK ){
      rc = multiCursorAddTree(pCsr, pDb->pWorker, eTree);
    }
    if( rc==LSM_OK 
        && eTree!=TREE_NONE
        && pNext && pNext->pMerge==0 && pNext->lhs.iRoot 

    ){
      pDel = &pNext->lhs;
      rc = btreeCursorNew(pDb, pDel, &pCsr->pBtCsr);
    }

    if( pNext==0 ){
      multiCursorIgnoreDelete(pCsr);
................................................................................
    Merge merge;                  /* Merge object used to create new level */
    MergeWorker mergeworker;      /* MergeWorker object for the same purpose */

    memset(&merge, 0, sizeof(Merge));
    memset(&mergeworker, 0, sizeof(MergeWorker));

    pNew->pMerge = &merge;
    pNew->iAge = -1;
    mergeworker.pDb = pDb;
    mergeworker.pLevel = pNew;
    mergeworker.pCsr = pCsr;
    pCsr->pPrevMergePtr = &iLeftPtr;

    /* Mark the separators array for the new level as a "phantom". */
    mergeworker.bFlush = 1;
................................................................................
    while( rc==LSM_OK && mergeWorkerDone(&mergeworker)==0 ){
      rc = mergeWorkerStep(&mergeworker);
    }
    assert( rc!=LSM_OK || mergeworker.nWork==0 || pNew->lhs.iFirst );

    nWrite = mergeworker.nWork;
    mergeWorkerShutdown(&mergeworker, &rc);




    pNew->pMerge = 0;
    pNew->iAge = 0;
  }

  if( rc!=LSM_OK || pNew->lhs.iFirst==0 ){
    assert( rc!=LSM_OK || pDb->pWorker->freelist.nEntry==0 );
    lsmDbSnapshotSetLevel(pDb->pWorker, pNext);
    sortedFreeLevel(pDb->pEnv, pNew);
  }else{
    if( pDel ) pDel->iRoot = 0;

#if 0
    lsmSortedDumpStructure(pDb, pDb->pWorker, 1, 0, "new-toplevel");
#endif

    if( freelist.nEntry ){
      Freelist *p = &pDb->pWorker->freelist;
      lsmFree(pDb->pEnv, p->aEntry);
      memcpy(p, &freelist, sizeof(freelist));
      freelist.aEntry = 0;
................................................................................
  /* Allocate the new Level object */
  pNew = (Level *)lsmMallocZeroRc(pDb->pEnv, sizeof(Level), &rc);
  if( pNew ){
    pNew->aRhs = (Segment *)lsmMallocZeroRc(pDb->pEnv, 
                                        nMerge * sizeof(Segment), &rc);
  }


  /* Populate the new Level object */
  if( rc==LSM_OK ){
    Level *pNext = 0;             /* Level following pNew */
    int i;

    Level *pTopLevel;
    Level *p = pLevel;
    Level **pp;
    pNew->nRight = nMerge;
    pNew->iAge = pLevel->iAge+1;
    for(i=0; i<nMerge; i++){
      assert( p->nRight==0 );
      pNext = p->pNext;
      pNew->aRhs[i] = p->lhs;

      sortedFreeLevel(pDb->pEnv, p);
      p = pNext;
    }



    /* Replace the old levels with the new. */
    pTopLevel = lsmDbSnapshotLevel(pDb->pWorker);
    pNew->pNext = p;
    for(pp=&pTopLevel; *pp!=pLevel; pp=&((*pp)->pNext));
    *pp = pNew;
    lsmDbSnapshotSetLevel(pDb->pWorker, pTopLevel);
................................................................................
  }
  if( nThis>nBest ){
    assert( pThis );
    pBest = pThis;
    nBest = nThis;
  }

  if( pBest==0 && nMerge==1 && pTopLevel && pTopLevel->pNext ){











    pBest = pTopLevel;
    nBest = 2;

  }

  if( pBest ){
    if( pBest->nRight==0 ){
      rc = sortedMergeSetup(pDb, pBest, nBest, ppOut);
    }else{
      *ppOut = pBest;
................................................................................
      /* Clean up the MergeWorker object initialized above. If no error
      ** has occurred, invoke the work-hook to inform the application that
      ** the database structure has changed. */
      mergeWorkerShutdown(&mergeworker, &rc);
      if( rc==LSM_OK ) sortedInvokeWorkHook(pDb);

#if 0
      lsmSortedDumpStructure(pDb, pDb->pWorker, 1, 0, "work");
#endif
      assertBtreeOk(pDb, &pLevel->lhs);
      assertRunInOrder(pDb, &pLevel->lhs);

      /* If bFlush is true and the database is no longer considered "full",
      ** break out of the loop even if nRemaining is still greater than
      ** zero. The caller has an in-memory tree to flush to disk.  */
................................................................................
          fileToString(pDb->pEnv, zLeft, sizeof(zLeft), 28, aLeft[i]); 
        }
        if( i<nRight ){ 
          fileToString(pDb->pEnv, zRight, sizeof(zRight), 28, aRight[i]); 
        }

        if( i==0 ){
          sqlite4_snprintf(zLevel, sizeof(zLevel), "L%d: (age=%d)", 
              iLevel, pLevel->iAge
          );
        }else{
          zLevel[0] = '\0';
        }

        if( nRight==0 ){
          iPad = 28 - (strlen(zLeft)/2) ;

static int multiCursorAddAll(MultiCursor *pCsr, Snapshot *pSnap){
  Level *pLvl;
  int nPtr = 0;
  int iPtr = 0;
  int rc = LSM_OK;

  for(pLvl=pSnap->pLevel; pLvl; pLvl=pLvl->pNext){
    /* If the LEVEL_INCOMPLETE flag is set, then this function is being
    ** called (indirectly) from within a sortedNewToplevel() call to
    ** construct pLvl. In this case ignore pLvl - this cursor is going to
    ** be used to retrieve a freelist entry from the LSM, and the partially
    ** complete level may confuse it.  */
    if( pLvl->flags & LEVEL_INCOMPLETE ) continue;
    nPtr += (1 + pLvl->nRight);
  }

  assert( pCsr->aPtr==0 );
  pCsr->aPtr = lsmMallocZeroRc(pCsr->pDb->pEnv, sizeof(SegmentPtr) * nPtr, &rc);
  if( rc==LSM_OK ) pCsr->nPtr = nPtr;

  for(pLvl=pSnap->pLevel; pLvl && rc==LSM_OK; pLvl=pLvl->pNext){
    int i;
    if( pLvl->flags & LEVEL_INCOMPLETE ) continue;
    pCsr->aPtr[iPtr].pLevel = pLvl;
    pCsr->aPtr[iPtr].pSeg = &pLvl->lhs;
    iPtr++;
    for(i=0; i<pLvl->nRight; i++){
      pCsr->aPtr[iPtr].pLevel = pLvl;
      pCsr->aPtr[iPtr].pSeg = &pLvl->aRhs[i];
      iPtr++;
................................................................................
  if( pCsr ){
    pCsr->pDb = pDb;
    rc = multiCursorVisitFreelist(pCsr);
    if( rc==LSM_OK ){
      rc = multiCursorAddTree(pCsr, pDb->pWorker, eTree);
    }
    if( rc==LSM_OK 

        && pNext && pNext->pMerge==0 && pNext->lhs.iRoot 
        && (eTree!=TREE_NONE || (pNext->flags & LEVEL_FREELIST_ONLY))
    ){
      pDel = &pNext->lhs;
      rc = btreeCursorNew(pDb, pDel, &pCsr->pBtCsr);
    }

    if( pNext==0 ){
      multiCursorIgnoreDelete(pCsr);
................................................................................
    Merge merge;                  /* Merge object used to create new level */
    MergeWorker mergeworker;      /* MergeWorker object for the same purpose */

    memset(&merge, 0, sizeof(Merge));
    memset(&mergeworker, 0, sizeof(MergeWorker));

    pNew->pMerge = &merge;
    pNew->flags |= LEVEL_INCOMPLETE;
    mergeworker.pDb = pDb;
    mergeworker.pLevel = pNew;
    mergeworker.pCsr = pCsr;
    pCsr->pPrevMergePtr = &iLeftPtr;

    /* Mark the separators array for the new level as a "phantom". */
    mergeworker.bFlush = 1;
................................................................................
    while( rc==LSM_OK && mergeWorkerDone(&mergeworker)==0 ){
      rc = mergeWorkerStep(&mergeworker);
    }
    assert( rc!=LSM_OK || mergeworker.nWork==0 || pNew->lhs.iFirst );

    nWrite = mergeworker.nWork;
    mergeWorkerShutdown(&mergeworker, &rc);
    pNew->flags &= ~LEVEL_INCOMPLETE;
    if( eTree==TREE_NONE ){
      pNew->flags |= LEVEL_FREELIST_ONLY;
    }
    pNew->pMerge = 0;

  }

  if( rc!=LSM_OK || pNew->lhs.iFirst==0 ){
    assert( rc!=LSM_OK || pDb->pWorker->freelist.nEntry==0 );
    lsmDbSnapshotSetLevel(pDb->pWorker, pNext);
    sortedFreeLevel(pDb->pEnv, pNew);
  }else{
    if( pDel ) pDel->iRoot = 0;

#if 0
    lsmSortedDumpStructure(pDb, pDb->pWorker, 0, 0, "new-toplevel");
#endif

    if( freelist.nEntry ){
      Freelist *p = &pDb->pWorker->freelist;
      lsmFree(pDb->pEnv, p->aEntry);
      memcpy(p, &freelist, sizeof(freelist));
      freelist.aEntry = 0;
................................................................................
  /* Allocate the new Level object */
  pNew = (Level *)lsmMallocZeroRc(pDb->pEnv, sizeof(Level), &rc);
  if( pNew ){
    pNew->aRhs = (Segment *)lsmMallocZeroRc(pDb->pEnv, 
                                        nMerge * sizeof(Segment), &rc);
  }


  /* Populate the new Level object */
  if( rc==LSM_OK ){
    Level *pNext = 0;             /* Level following pNew */
    int i;
    int bFreeOnly = 1;
    Level *pTopLevel;
    Level *p = pLevel;
    Level **pp;
    pNew->nRight = nMerge;
    pNew->iAge = pLevel->iAge+1;
    for(i=0; i<nMerge; i++){
      assert( p->nRight==0 );
      pNext = p->pNext;
      pNew->aRhs[i] = p->lhs;
      if( (p->flags & LEVEL_FREELIST_ONLY)==0 ) bFreeOnly = 0;
      sortedFreeLevel(pDb->pEnv, p);
      p = pNext;
    }

    if( bFreeOnly ) pNew->flags |= LEVEL_FREELIST_ONLY;

    /* Replace the old levels with the new. */
    pTopLevel = lsmDbSnapshotLevel(pDb->pWorker);
    pNew->pNext = p;
    for(pp=&pTopLevel; *pp!=pLevel; pp=&((*pp)->pNext));
    *pp = pNew;
    lsmDbSnapshotSetLevel(pDb->pWorker, pTopLevel);
................................................................................
  }
  if( nThis>nBest ){
    assert( pThis );
    pBest = pThis;
    nBest = nThis;
  }

  if( pBest==0 && nMerge==1 ){
    int nFree = 0;
    int nUsr = 0;
    for(pLevel=pTopLevel; pLevel; pLevel=pLevel->pNext){
      assert( !pLevel->nRight );
      if( pLevel->flags & LEVEL_FREELIST_ONLY ){
        nFree++;
      }else{
        nUsr++;
      }
    }
    if( nUsr>1 ){
      pBest = pTopLevel;
      nBest = nFree + nUsr;
    }
  }

  if( pBest ){
    if( pBest->nRight==0 ){
      rc = sortedMergeSetup(pDb, pBest, nBest, ppOut);
    }else{
      *ppOut = pBest;
................................................................................
      /* Clean up the MergeWorker object initialized above. If no error
      ** has occurred, invoke the work-hook to inform the application that
      ** the database structure has changed. */
      mergeWorkerShutdown(&mergeworker, &rc);
      if( rc==LSM_OK ) sortedInvokeWorkHook(pDb);

#if 0
      lsmSortedDumpStructure(pDb, pDb->pWorker, 0, 0, "work");
#endif
      assertBtreeOk(pDb, &pLevel->lhs);
      assertRunInOrder(pDb, &pLevel->lhs);

      /* If bFlush is true and the database is no longer considered "full",
      ** break out of the loop even if nRemaining is still greater than
      ** zero. The caller has an in-memory tree to flush to disk.  */
................................................................................
          fileToString(pDb->pEnv, zLeft, sizeof(zLeft), 28, aLeft[i]); 
        }
        if( i<nRight ){ 
          fileToString(pDb->pEnv, zRight, sizeof(zRight), 28, aRight[i]); 
        }

        if( i==0 ){
          sqlite4_snprintf(zLevel, sizeof(zLevel), "L%d: (age=%d) (flags=%.4x)",
              iLevel, (int)pLevel->iAge, (int)pLevel->flags
          );
        }else{
          zLevel[0] = '\0';
        }

        if( nRight==0 ){
          iPad = 28 - (strlen(zLeft)/2) ;

  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   --  4K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   --  8K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 16K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 32K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 64K
}
do_test 3.2 {

  sqlite4_lsm_work db main -nmerge 1 -npage 1000000
  execsql { SELECT count(*) FROM t1 }
} {65536}
do_test 3.3 {
  db close
  sqlite4 db test.db
  execsql { SELECT count(*) FROM t1 }
} {65536}
do_test 3.4 {
  execsql { INSERT INTO t1 VALUES(randstr(100,100), randstr(100,100)) }

  sqlite4_lsm_work db main -nmerge 1 -npage 1000000
  execsql { SELECT count(*) FROM t1 }
} {65537}

finish_test

  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   --  4K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   --  8K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 16K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 32K
  INSERT INTO t1 SELECT randstr(100,100), randstr(100,100) FROM t1;   -- 64K
}
do_test 3.2 {
  sqlite4_lsm_flush db main
  sqlite4_lsm_work db main -nmerge 1 -npage 1000000
  execsql { SELECT count(*) FROM t1 }
} {65536}
do_test 3.3 {
  db close
  sqlite4 db test.db
  execsql { SELECT count(*) FROM t1 }
} {65536}
do_test 3.4 {
  execsql { INSERT INTO t1 VALUES(randstr(100,100), randstr(100,100)) }
  sqlite4_lsm_flush db main
  sqlite4_lsm_work db main -nmerge 1 -npage 1000000
  execsql { SELECT count(*) FROM t1 }
} {65537}

finish_test

populate_db

do_execsql_test 1.1 { SELECT * FROM t1 } {
  0 0 1 1 2 4 3 9 4 16 5 25 6 36 7 49 8 64 9 81
}
db eval { SELECT a, b FROM t1 } {
  do_test 1.2.1 { 
    list [catch { sqlite4_lsm_work db main 0 } msg] $msg
  } {1 SQLITE4_MISUSE}
  do_test 1.2.2 { 
    list [catch { sqlite4_lsm_work db main 1 } msg] $msg
  } {1 SQLITE4_MISUSE}
  break
}


#-------------------------------------------------------------------------
#
................................................................................
}
do_test 2.2 { 
  sqlite4 db2 ./test.db
  list [catch { db2 eval { BEGIN ; INSERT INTO t1 VALUES(1, 2) } } msg] $msg
} {1 {database is locked}}

do_execsql_test 2.3 { COMMIT }
do_test 2.4 { sqlite4_lsm_work db2 main 0 } {0}
db2 close


#-------------------------------------------------------------------------
# Check that if a transaction is committed and this causes the in-memory
# tree to be flushed to disk, 
#

populate_db

do_execsql_test 1.1 { SELECT * FROM t1 } {
  0 0 1 1 2 4 3 9 4 16 5 25 6 36 7 49 8 64 9 81
}
db eval { SELECT a, b FROM t1 } {
  do_test 1.2.1 { 
    list [catch { sqlite4_lsm_work db main -nmerge 2 -npage 10 } msg] $msg
  } {1 SQLITE4_MISUSE}
  do_test 1.2.2 { 
    list [catch { sqlite4_lsm_work db main -nmerge 2 -npage 10 } msg] $msg
  } {1 SQLITE4_MISUSE}
  break
}


#-------------------------------------------------------------------------
#
................................................................................
}
do_test 2.2 { 
  sqlite4 db2 ./test.db
  list [catch { db2 eval { BEGIN ; INSERT INTO t1 VALUES(1, 2) } } msg] $msg
} {1 {database is locked}}

do_execsql_test 2.3 { COMMIT }
do_test 2.4 { sqlite4_lsm_work db2 main -npage 0 } {0}
db2 close


#-------------------------------------------------------------------------
# Check that if a transaction is committed and this causes the in-memory
# tree to be flushed to disk, 
#