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Comment:Require a minimum fanout for interior nodes. This prevents cases where excessively large terms keep the tree from finding a single root. A downside is that this could result in large interior nodes in the presence of large terms, which may be prone to fragmentation, though if the nodes were smaller that would translate into more levels in the tree, which would also have that problem. (CVS 3510)
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SHA1:64b7e3406134ac4891113b9bb432ad97504268bb
User & Date: shess 2006-11-13 21:00:55
Context
2006-11-13
21:09
Delta-encode docids. This is good for around 22% reduction in index size with DL_POSITIONS. It improves performance about 5%-6%. (CVS 3511) check-in: 9b6d413d user: shess tags: trunk
21:00
Require a minimum fanout for interior nodes. This prevents cases where excessively large terms keep the tree from finding a single root. A downside is that this could result in large interior nodes in the presence of large terms, which may be prone to fragmentation, though if the nodes were smaller that would translate into more levels in the tree, which would also have that problem. (CVS 3510) check-in: 64b7e340 user: shess tags: trunk
20:15
Allow backing tables to be missing on dropping fts table. Fixes http://www.sqlite.org/cvstrac/tktview?tn=1992,35 . (CVS 3509) check-in: 9628a61a user: shess tags: trunk
Changes
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Changes to ext/fts2/fts2.c.

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** is encoded.  The subtree at iBlockid will contain all terms less
** than the first term encoded (or all terms if no term is encoded).
** Otherwise, for terms greater than or equal to pTerm[i] but less
** than pTerm[i+1], the subtree for that term will be rooted at
** iBlockid+i.
**
** New data is spilled to a new interior node at the same height when
** the current node exceeds INTERIOR_MAX bytes (default 2048).  The


** interior nodes at a given height are naturally tracked by interior
** nodes at height+1, and so on.
**
**
**** Segment directory ****
** The segment directory in table %_segdir stores meta-information for
** merging and deleting segments, and also the root node of the
** segment's tree.
**
................................................................................
/* InteriorWriter is used to collect terms and block references into
** interior nodes in %_segments.  See commentary at top of file for
** format.
*/

/* How large interior nodes can grow. */
#define INTERIOR_MAX 2048











/* ROOT_MAX controls how much data is stored inline in the segment
** directory.
*/
/* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
** only here so that interiorWriterRootInfo() and leafWriterRootInfo()
** can both see it, but if the caller passed it in, we wouldn't even
................................................................................
}

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
  struct InteriorWriter *parentWriter;


#ifndef NDEBUG
  sqlite_int64 iLastChildBlock;  /* for consistency checks. */
#endif
} InteriorWriter;

/* Initialize an interior node where pTerm[nTerm] marks the leftmost
** term in the tree.  iChildBlock is the leftmost child block at the
................................................................................
                               sqlite_int64 iChildBlock,
                               InteriorWriter *pWriter){
  InteriorBlock *block;
  assert( iHeight>0 );
  CLEAR(pWriter);

  pWriter->iHeight = iHeight;

#ifndef NDEBUG
  pWriter->iLastChildBlock = iChildBlock;
#endif
  block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
  pWriter->last = pWriter->first = block;
}

................................................................................
  int n = putVarint(c, nTerm);

#ifndef NDEBUG
  pWriter->iLastChildBlock++;
#endif
  assert( pWriter->iLastChildBlock==iChildBlock );




  if( pWriter->last->data.nData+n+nTerm>INTERIOR_MAX ){
    /* Overflow to a new block. */

    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;

  }else{
    dataBufferAppend2(&pWriter->last->data, c, n, pTerm, nTerm);
  }
}

/* Free the space used by pWriter, including the linked-list of
** InteriorBlocks, and parentWriter, if present.







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** is encoded.  The subtree at iBlockid will contain all terms less
** than the first term encoded (or all terms if no term is encoded).
** Otherwise, for terms greater than or equal to pTerm[i] but less
** than pTerm[i+1], the subtree for that term will be rooted at
** iBlockid+i.
**
** New data is spilled to a new interior node at the same height when
** the current node exceeds INTERIOR_MAX bytes (default 2048).
** INTERIOR_MIN_TERMS (default 7) keeps large terms from monopolizing
** interior nodes and making the tree too skinny.  The interior nodes
** at a given height are naturally tracked by interior nodes at
** height+1, and so on.
**
**
**** Segment directory ****
** The segment directory in table %_segdir stores meta-information for
** merging and deleting segments, and also the root node of the
** segment's tree.
**
................................................................................
/* InteriorWriter is used to collect terms and block references into
** interior nodes in %_segments.  See commentary at top of file for
** format.
*/

/* How large interior nodes can grow. */
#define INTERIOR_MAX 2048

/* Minimum number of terms per interior node (except the root). This
** prevents large terms from making the tree too skinny - must be >0
** so that the tree always makes progress.  Note that the min tree
** fanout will be INTERIOR_MIN_TERMS+1.
*/
#define INTERIOR_MIN_TERMS 7
#if INTERIOR_MIN_TERMS<1
# error INTERIOR_MIN_TERMS must be greater than 0.
#endif

/* ROOT_MAX controls how much data is stored inline in the segment
** directory.
*/
/* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
** only here so that interiorWriterRootInfo() and leafWriterRootInfo()
** can both see it, but if the caller passed it in, we wouldn't even
................................................................................
}

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
  struct InteriorWriter *parentWriter;

  sqlite_int64 iOpeningChildBlock; /* First child block in block "last". */
#ifndef NDEBUG
  sqlite_int64 iLastChildBlock;  /* for consistency checks. */
#endif
} InteriorWriter;

/* Initialize an interior node where pTerm[nTerm] marks the leftmost
** term in the tree.  iChildBlock is the leftmost child block at the
................................................................................
                               sqlite_int64 iChildBlock,
                               InteriorWriter *pWriter){
  InteriorBlock *block;
  assert( iHeight>0 );
  CLEAR(pWriter);

  pWriter->iHeight = iHeight;
  pWriter->iOpeningChildBlock = iChildBlock;
#ifndef NDEBUG
  pWriter->iLastChildBlock = iChildBlock;
#endif
  block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
  pWriter->last = pWriter->first = block;
}

................................................................................
  int n = putVarint(c, nTerm);

#ifndef NDEBUG
  pWriter->iLastChildBlock++;
#endif
  assert( pWriter->iLastChildBlock==iChildBlock );

  /* Overflow to a new block if the new term makes the current block
  ** too big, and the current block already has enough terms.
  */
  if( pWriter->last->data.nData+n+nTerm>INTERIOR_MAX &&

      iChildBlock-pWriter->iOpeningChildBlock>INTERIOR_MIN_TERMS ){
    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;
    pWriter->iOpeningChildBlock = iChildBlock;
  }else{
    dataBufferAppend2(&pWriter->last->data, c, n, pTerm, nTerm);
  }
}

/* Free the space used by pWriter, including the linked-list of
** InteriorBlocks, and parentWriter, if present.