Thanks for your detailed explanation. for your first question: I mean creating a new database file.
since you asserted " >> innodb allows creating a db on a raw disk partition, can we do the >> same on sqlite? > > No. You need a file system of some kind. Or, at least, your operating > system needs to be able to address your storage using file-system calls, not > storage-structure calls. ", that answers my question. On Fri, Nov 19, 2010 at 5:38 AM, Simon Slavin <[email protected]> wrote: > > On 19 Nov 2010, at 7:04am, Yang wrote: > >> when I create a db on a file system, I guess a query process > > Wait ... are you talking here about creating a new database file or querying > one what already exists ? > >> has to go >> through 2 levels of seeks ? >> first sqlite finds the B-tree node that stores the index to the file >> offset of my desired record, then sqlite uses that offset to make >> syscall seek(offset), >> then Kernel consults the FS implementation to find from its OWN >> B-tree (for example in ext3 fs ) the block location of that offset. > > Assuming that you're using a FS that uses B-trees, nodes, and indices (many > don't), that's a fair summary of what happens. But SQLite runs fine on many > embedded systems that use linked lists instead of B-trees, or don't use > nodes, or have databases stored in non-writable sequential memory. > >> innodb allows creating a db on a raw disk partition, can we do the >> same on sqlite? > > No. You need a file system of some kind. Or, at least, your operating > system needs to be able to address your storage using file-system calls, not > storage-structure calls. > >> I tried directly creating a db on ramdisk, failed: >> >> javasqlite-20100727# sqlite3 /dev/ram0 > > You didn't tell it what to call the database, just where you wanted it. I > think you want something like > > # sqlite3 /dev/ram0/myDatabase.sqlite > > There's no reason this shouldn't work if your drivers and your version of > *n*x /fully/ support the use of /deb/ram0 for file storage, including support > for locking calls. Works fine under Mac OS X, by the way. > > But SQLite does provide its own way of creating a database in memory. See > > http://www.sqlite.org/inmemorydb.html > > So you'd use something like > > # sqlite3 :memory: > > Of course, that database will be visible only to the process that creates it. > Which means that if you use the command-line tool to create it it will > effectively disappear as you quit the command-line tool. > > If you're using Linux or a Unix that supports it, you can also look into the > shared memory filesystem 'tmpfs'. I haven't tried it, but this should also > support SQLite without any problems. > > Simon. > _______________________________________________ > sqlite-users mailing list > [email protected] > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
