The speed of a virtual table depends on the backing store and software used to implement it.
We have virtual tables that reference CTree files as well as virtual tables that reference memory sections here. The advantage is that the VT implementation can adjust it's answers in the xBestIndex function. -----Ursprüngliche Nachricht----- Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im Auftrag von Dominique Devienne Gesendet: Mittwoch, 24. Juli 2019 10:02 An: SQLite mailing list <sqlite-users@mailinglists.sqlite.org> Betreff: [EXTERNAL] Re: [sqlite] Estimated Costs and Memory DBs On Wed, Jul 24, 2019 at 2:55 AM Justin Olbrantz <justin.olbra...@gmail.com> wrote: > [...] my virtual table will be held completely in memory. What should > I do with the estimatedCost value from xBestIndex? According to the > documentation this should be an approximation of the number of disk > accesses for the query, which would be 0 in this case. But it's > clearly vastly faster to do a query on an indexed column, meaning the > cost for an indexed column should be much lower than the cost for an > unindexed column. How should I be doing this? > This is unfortunately similar to questions I asked on this ML in the past, with no good answers as far as I remember... For queries that mix "normal" disk-tables, in-memory-tables (i.e. the equivalent of a disk-table but with the DB file on a RAM disk, entirely in memory), and virtual-tables (e.g. accessing a C++ in-memory container of structs), the cost structure of these 3 are quite different. The last 2 are entirely in-memory both, yet the last case is quite a bit faster still (no decoding of pages/rows/varints needed). I confess to not studying the code to try to answer that myself though... --DD _______________________________________________ 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 | Klitschgasse 2-4, A-1130 Vienna | FN 157284 a, HG Wien, DVR: 0430013 | (O) +43 1 80100 - 0 May be privileged. May be confidential. Please delete if not the addressee. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
