Hello Pawel, you made some good points. I'm still in the stage of evaluation, I don't claim to know, its faster. But I saw that behavior on a filemanger: when you copy a large file, it immediately reseveres the whole space. The same with STL vectors: initializing it with a size is faster than growing it element by element. Therefor my question, if there is such a possibility.
> I wouldn't be so sure about that. Did anybody make any measurements? > 1) I don't know where do you think CPU cycles are saved but you > definitely get some more CPU cycles in maintaining free-list of pages > which will never be there if database grows page-by-page. Here I (or we) think of the cycles the system needs when the small niche of the initial database is exhausted and it has to look for another free block on the filesystem. If you can tell the system in advance, how big the niche has to be, it saves some time. > 2) Even if you use Martin's technique by creating some big blob why do > you think that SQLite will grow database file by necessary amount of > pages at once instead of page-by-page? And is there something in > SQLite's code that writes several sequential pages in one OS call > instead of writing them page-by-page? Thats indeed very uncertain. Here we have to look, how SQLite handles this. If you have a transaction, SQLite could look, how much more space is needed and preallocate this. > I can agree that making file grow in one big piece instead of many > small ones seems to compact most IO into one call instead of many. But > will it be somehow faster? I doubt it. And bear in mind that all your > efforts can be immediately trashed away by another process reading > some big file(s) which will consume all OS file cache, so OS will have > to re-read your database file later when you actually need it. This > way I guess overall number of IO operations on the system will only > increase... That might be. We just can prove it one way: measure, measure, measure. I also don't expect huge performance increases, but if it is some percent with little effort.. It could be worth it. Thomas _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
