On 8/11/17, Scott Robison <sc...@casaderobison.com> wrote: > My understanding is that SQLite doesn't use the traditional definition of > b-tree because it doesn't use fixed size records/keys. It will cram as few > or as many as possible.
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Correct. More records crammed into one page means that fewer pages need to be read, which makes things run faster. It also means that less disk space gets used. The in-tree portion of each record is size limited to ensure that at least four records fit on each page. Otherwise, the btree might degenerate into a linked list. The tail of records that exceed the maximum in-tree record size is written onto overflow pages. For ordinary rowid tables, a traditional b-tree is used, which means that only the key is stored on intermediate pages and all the content appears in the leaves. Since the keys are always just a rowid and typically take only a few bytes, there are ordinarily a large number keys per page. You can run the sqlite3_analyzer.exe utility program (available in the "sqlite-tools-*" bundles on the https://sqlite.org/download.html page) to see the average number of keys/page for each table and index. Or you can use the DBSTAT virtual table (https://www.sqlite.org/dbstat.html) to query for that information on a page-by-page basis. For indexes and WITHOUT ROWID tables, the keys can be much larger, and so the minimum-four-per-page rule is more likely to come into play. -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
