In the "SQLite File Format" document, the BTree layout is described, but now I want to know how to get the BTree level (which is the 'K' value mentioned in the Documentation)?
Generally, one B+Tree segment contains K keys and (K+1) pointers to child segments. From the source code, I found such info: /* ** This constant controls how often segments are merged. Once there are ** FTS3_MERGE_COUNT segments of level N, they are merged into a single ** segment of level N+1. */ #define FTS3_MERGE_COUNT 16 .... /* ** FTS4 virtual tables may maintain multiple indexes - one index of all terms ** in the document set and zero or more prefix indexes. All indexes are stored ** as one or more b+-trees in the %_segments and %_segdir tables. ** ** It is possible to determine which index a b+-tree belongs to based on the ** value stored in the "%_segdir.level" column. Given this value L, the index ** that the b+-tree belongs to is (L<<10). In other words, all b+-trees with ** level values between 0 and 1023 (inclusive) belong to index 0, all levels ** between 1024 and 2047 to index 1, and so on. ** ** It is considered impossible for an index to use more than 1024 levels. In ** theory though this may happen, but only after at least ** (FTS3_MERGE_COUNT^1024) separate flushes of the pending-terms tables. */ #define FTS3_SEGDIR_MAXLEVEL 1024 #define FTS3_SEGDIR_MAXLEVEL_STR "1024" It seems the BTree level is 16 or 1024 ?? Would any one share you knowledge on how to get this value ? Much appreciated if you can tell how to tune this value. Thanks! _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
