Thanks, but I'm more confused now.
As in the example that I provided, there are 4 cells in a single btree page. So there must be some mechanism to determine hoe many keys that one cell can own. I want to know exactly the very value and just how to change the value to a larger one, for example, 256, 512, or even larger. ________________________________ From: sqlite-users <sqlite-users-boun...@mailinglists.sqlite.org> on behalf of Hick Gunter <h...@scigames.at> Sent: Friday, August 11, 2017 16:31 To: 'SQLite mailing list' Subject: Re: [sqlite] What's the level of B+-Tree ? The number of keys in an sqlite index page depends on the size of the database pages and the size of the (compressed) key value, which is stored in the same "row format" as the data. Child segment pointers are stored at the beginning of the page and key contents are stored at the end. The page is full, when the unallocated space in between these areas becomes too small to store enything useful. Note that key contents may change in length if a key field is updated, so the key contents area may become fragmented (sqlite willl defragment the page if needed). -----Ursprüngliche Nachricht----- Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im Auftrag von ni james Gesendet: Freitag, 11. August 2017 04:57 An: sqlite-users@mailinglists.sqlite.org Betreff: [sqlite] What's the level of B+-Tree ? 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 ___________________________________________ Gunter Hick Software Engineer Scientific Games International GmbH FN 157284 a, HG Wien Klitschgasse 2-4, A-1130 Vienna, Austria Tel: +43 1 80100 0 E-Mail: h...@scigames.at This communication (including any attachments) is intended for the use of the intended recipient(s) only and may contain information that is confidential, privileged or legally protected. Any unauthorized use or dissemination of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by return e-mail message and delete all copies of the original communication. Thank you for your cooperation. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
