On Mon, Jun 25, 2012 at 10:05 PM, Bo Peng <ben....@gmail.com> wrote: >> Are these multiple tables in a single database (file), or multiple databases >> (files)? Multiple connections or a single connection? > > Right now there are multiple read-only processes to read the same > file. If I go with any RAM-based solution, I will have to use a single > process to read database and feed the data to calculation processes. > >> In any case, you set the cache size in pages by executing "PRAGMA >> cache_size=<pages>" after opening the database connection. >> >> You can test it without modifying your code by executing "PRAGMA >> default_cache_size=<pages>;" against the database file using the shell. >> >> The default sqlite page cache per database connection is 2000 pages. So the >> maximum memory used by sqlite for the page cache is page_size * cache_size. >> You can query these with "pragma page_size" and query/set the cache size >> with "pragma cache_size". > > This is a great idea because ideally I can load all database to cache > if there are enough RAM. However, I am wondering if extra-large cache > might actually hurt the performance if cached pages have to be > consecutive. I mean, if there are 100,000 pages and I specify a cache > to hold 40,000 pages. When I get the first and last table, will sqlite > load the first 40,000 pages, read the first table, read the last > 40,000 pages, and load the last table? I guess (and hope) sqlite is > cleverer than that...
Yes, SQLite is better than that. Even for one table it loads into cache only those pages which are needed to execute query, nothing more. Pavel _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
