Update comments in fts3.c to more accurately describe the doclist format.
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@ -23,9 +23,6 @@
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** SQLite (in which case SQLITE_ENABLE_FTS3 is defined).
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*/
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/* TODO(shess) Consider exporting this comment to an HTML file or the
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** wiki.
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*/
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/* The full-text index is stored in a series of b+tree (-like)
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** structures called segments which map terms to doclists. The
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** structures are like b+trees in layout, but are constructed from the
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@ -48,13 +45,27 @@
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** 21 bits - BBA
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** and so on.
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**
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** This is identical to how sqlite encodes varints (see util.c).
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** This is similar in concept to how sqlite encodes "varints" but
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** the encoding is not the same. SQLite varints are big-endian
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** are are limited to 9 bytes in length whereas FTS3 varints are
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** little-endian and can be upt to 10 bytes in length (in theory).
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**
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** Example encodings:
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**
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** 1: 0x01
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** 127: 0x7f
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** 128: 0x81 0x00
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**
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**
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**** Document lists ****
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** A doclist (document list) holds a docid-sorted list of hits for a
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** given term. Doclists hold docids, and can optionally associate
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** token positions and offsets with docids.
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** token positions and offsets with docids. A position is the index
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** of a word within the document. The first word of the document has
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** a position of 0.
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**
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** FTS3 used to optionally store character offsets using a compile-time
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** option. But that functionality is no longer supported.
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**
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** A DL_POSITIONS_OFFSETS doclist is stored like this:
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**
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@ -62,16 +73,12 @@
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** varint docid;
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** array { (position list for column 0)
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** varint position; (delta from previous position plus POS_BASE)
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** varint startOffset; (delta from previous startOffset)
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** varint endOffset; (delta from startOffset)
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** }
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** array {
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** varint POS_COLUMN; (marks start of position list for new column)
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** varint column; (index of new column)
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** array {
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** varint position; (delta from previous position plus POS_BASE)
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** varint startOffset;(delta from previous startOffset)
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** varint endOffset; (delta from startOffset)
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** }
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** }
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** varint POS_END; (marks end of positions for this document.
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@ -79,10 +86,23 @@
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**
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** Here, array { X } means zero or more occurrences of X, adjacent in
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** memory. A "position" is an index of a token in the token stream
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** generated by the tokenizer, while an "offset" is a byte offset,
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** both based at 0. Note that POS_END and POS_COLUMN occur in the
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** same logical place as the position element, and act as sentinals
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** ending a position list array.
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** generated by the tokenizer. Note that POS_END and POS_COLUMN occur
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** in the same logical place as the position element, and act as sentinals
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** ending a position list array. POS_END is 0. POS_COLUMN is 1.
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** The positions numbers are not stored literally but rather as two more
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** the difference from the prior position, or the just the position plus
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** 2 for the first position. Example:
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**
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** label: A B C D E F G H I J K
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** value: 123 5 9 1 1 14 35 0 234 72 0
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**
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** The 123 value is the first docid. For column zero in this document
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** there are two matches at positions 3 and 10 (5-2 and 9-2+3). The 1
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** at D signals the start of a new column; the 1 at E indicates that the
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** new column is column number 1. There are two positions at 12 and 45
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** (14-2 and 35-2+12). The 0 at H indicate the end-of-document. The
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** 234 at I is the next docid. It has one position 72 (72-2) and then
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** terminates with the 0 at K.
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**
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** A DL_POSITIONS doclist omits the startOffset and endOffset
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** information. A DL_DOCIDS doclist omits both the position and
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@ -388,12 +408,23 @@ void sqlite3Fts3Dequote(char *z){
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}
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}
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/*
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** Read a single varint from the doclist at *pp and advance *pp to point
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** to the next element of the varlist. Add the value of the varint
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** to *pVal.
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*/
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static void fts3GetDeltaVarint(char **pp, sqlite3_int64 *pVal){
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sqlite3_int64 iVal;
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*pp += sqlite3Fts3GetVarint(*pp, &iVal);
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*pVal += iVal;
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}
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/*
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** As long as *pp has not reached its end (pEnd), then do the same
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** as fts3GetDeltaVarint(): read a single varint and add it to *pVal.
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** But if we have reached the end of the varint, just set *pp=0 and
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** leave *pVal unchanged.
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*/
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static void fts3GetDeltaVarint2(char **pp, char *pEnd, sqlite3_int64 *pVal){
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if( *pp>=pEnd ){
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*pp = 0;
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@ -782,12 +813,6 @@ static int fts3OpenMethod(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCsr){
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return SQLITE_OK;
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}
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/****************************************************************/
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/****************************************************************/
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/****************************************************************/
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/****************************************************************/
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/*
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** Close the cursor. For additional information see the documentation
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** on the xClose method of the virtual table interface.
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24
manifest
24
manifest
@ -1,5 +1,8 @@
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C Added\soption\sto\sdump\spages.
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D 2010-01-08T04:50:22
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-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA1
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C Update\scomments\sin\sfts3.c\sto\smore\saccurately\sdescribe\sthe\sdoclist\sformat.
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D 2010-01-08T23:01:33
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F Makefile.in c5827ead754ab32b9585487177c93bb00b9497b3
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F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
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@ -56,7 +59,7 @@ F ext/fts2/mkfts2amal.tcl 974d5d438cb3f7c4a652639262f82418c1e4cff0
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F ext/fts3/fts3_expr.c f4ff02ebe854e97ac03ff00b38b728a9ab57fd4b
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@ -785,7 +788,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
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@ -1 +1 @@
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e424a0307359fee6875424c10ecad1a10acfba0e
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