Ideally, at least on non-CE platforms, I'd like see SQLite not give the OS any hints about caching. However, I'm not sure what kind of performance hit (if any) that would have on Windows. It's already been proven that providing the hint on WinCE is beneficial.
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Roger Binns Sent: Wednesday, September 17, 2008 2:02 PM To: General Discussion of SQLite Database Subject: Re: [sqlite] Vista frustrations -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Robert Simpson wrote: > The purpose of a cache is to improve performance and responsiveness. Any > cache that uses all physical memory, forces all other apps to the paging > file All current operating systems do this, using heuristics to determine how much of each running application to leave in memory while using "spare" memory for filesystem cache and dynamically changing allocation based on demand. Sometimes they mess up to the detriment of idle applications. However that is not the bit I am talking about as it is not controlled by flags when opening files and instead is part of the core operating system code. (You often see this issue when copying files larger than RAM). What is under discussion is how the operating system is using the cache that it does decide to allocate for SQLite. If you tell it that a file is sequential access then that means that read ahead is good and that data already read can be discarded. If you tell it that a file is random access then read ahead is bad (it has the disk occupied when the next random request comes in) and already read data should be kept. SQLite does not know and should be leaving it up to the operating system. Your tests prove that when that is done on Vista, performance of SQLite is better and other applications are less adversely affected. > The real frustration is that this seems to be a rather obvious bug in Vista, > and definitely not SQLite's responsibility. This is conflating two issues. One is the tradeoff between RAM usage for cache vs idle applications. You can argue that is a bug, or more accurately there are circumstances under which the tradeoff picks wrong values, and is very hard to get right. Example underlying details are at http://blogs.technet.com/markrussinovich/archive/2008/02/04/2826167.aspx The second issue is the performance differences when random access, sequential and no flags are given while opening the file and the resulting performance. In this case a file is accessed mostly sequentially but the random access flag is given. Performance was worse than letting the operating system use its own heuristics. That is hardly surprising or a bug. Roger -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFI0XBYmOOfHg372QQRAmKfAJ4pWVfZ8LS2ET+Y5CCCC5FGT3Am9wCfZg4e McaZrcLUXQJhU7i1Gw5+cRk= =CQg5 -----END PGP SIGNATURE----- _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
