>> Is there any >> reliable method to determine the minimum page-cache allocation size >> needed for a given page_size? >> > >sqlite3_status(SQLITE_STATUS_PAGECACHE_SIZE, ...)
Unfortunately, there is extra overhead involved which is not handled by the page cache but is allocated by malloc() if I understand correctly. From reading the sources (some weeks ago, the exact numbers might have changed) I determined an extra of at least 152 bytes are allocated for each page. Reference is nByteHdr in pager.c, plus an extra 4 byte (on 32 bit) for the slot the page hash (probably a little more to accommodate for empty slots). Interestingly, the page cache overhead size can differ between SQLite versions and also depends on SQLITE_OMIT_... compiler settings. 152 bytes might not seem much but this is nearly 15% for a page cache size of 1024 bytes, and nearly 30% for a 512 byte page cache. So you safe overhead by choosing a larger page size. Concluding, memory requirements are much higher than just pragma page_size * pragma cache_size This can sum up to lots of RAM when using page_size = 100000 or more to speed up indexing of very large databases. Users should be aware of this when running SQLite on extreme (low RAM or high size database) scenarios. Ralf _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
