OK. Curiosity is a good thing in certain situations. But could you kindly tell me what will you do with this information (assuming it's possible to obtain it of course)?
Pavel On Sat, Oct 27, 2012 at 11:54 PM, David Barrett <dbarr...@expensify.com> wrote: > I completely understand the wide and varied differences. I'm just *also* > interested in this very specific issue. > > -david > > On Sun, Oct 28, 2012 at 12:38 PM, Pavel Ivanov <paiva...@gmail.com> wrote: > >> > That said, I'd still welcome any quick summary of the differences between >> > sqlite and mysql when it comes to fragmentation. >> >> This is far from main differences between sqlite and mysql that you >> should consider if you want to choose between them unless of course >> your question is just about an academic interest. As you are talking >> about employees I guess you are not in some purely academic exercise. >> In this case think more about in-process code vs pumping through >> TCP/IP stack, designed mostly to be accessible from machine-local >> processes only vs accessible to anyone on the network, plain access to >> everything vs versatile and complicated authorization and >> authentication mechanisms, and so on and so forth. Database format is >> never a part of the decision which DBMS you want to use. >> >> Pavel >> >> >> On Sat, Oct 27, 2012 at 9:32 PM, David Barrett <dbarr...@expensify.com> >> wrote: >> > Thanks, this is really helpful! (And I lecture my employees about the >> > evils of premature optimization all the time. In fact, I'll lecture >> anyone >> > in earshot, so frequently that it's the butt of jokes.) >> > >> > That said, I'd still welcome any quick summary of the differences between >> > sqlite and mysql when it comes to fragmentation. I often get in debates >> > about sqlite versus other datbases, and I'm always eager to be informed. >> > Thanks! >> > >> > -david >> > >> > On Sat, Oct 27, 2012 at 11:42 PM, Simon Slavin <slav...@bigfraud.org> >> wrote: >> > >> >> >> >> On 27 Oct 2012, at 11:38am, David Barrett <dbarr...@expensify.com> >> wrote: >> >> >> >> > I'm trying to learn more about MySQL versus sqllite when it comes to >> >> > vacuuming and fragmentation, especially as it relates to SSD storage. >> >> >> >> >> >> Rather than answer your questions point-by-point, I'm going to give you >> >> the current state of play. Your understanding of how the various DBMSes >> >> work is right, but your excellent question "in a world with SSDs and a >> >> tremendous amount of RAM, does vacuuming matter nearly as much as on a >> >> spinning disk with constrained RAM?" cuts to the heart of all your other >> >> points. The following involves a little simplification and handwaving >> >> because otherwise it would be two chapters long and you'd have to do >> >> homework. >> >> >> >> Fragmentation made a big difference to apps running on Windows, but very >> >> little on any other platform. This is because Windows does something >> >> called 'read-ahead caching' which assumes that if you read block B, >> you're >> >> soon going to want to read block B+1, so at quite a low level it >> helpfully >> >> pre-reads it for you. Other operating systems don't make this >> assumption. >> >> This is why Windows users talk about defragmentation so much, but Unix >> >> users don't care about it. >> >> >> >> SSDs negate the whole point of defragmentation. On a rotational disk >> it's >> >> faster to read blocks B, B+1, B+2, B+4, B+5 than it is to read five >> random >> >> blocks from the disk, because the read heads are already positioned in >> the >> >> right place, and the disk is going to rotate to show those five blocks >> in >> >> order. SSDs are just like RAM: they're Random Access Memory. Reading >> any >> >> five blocks in any order takes roughly the same time. So nobody cares >> >> about fragmentation on an SSD. Read whatever blocks you want in >> whatever >> >> order you want. >> >> >> >> As to clever management of disk block alignment with respect to rows and >> >> columns, this is rarely worth attention these days. The amount of >> >> programming and debugging time it takes to get this right, and the >> amount >> >> of extra processing and disk access you need to do, give you less >> return on >> >> investment than if you spent the same money on buying a faster hard >> disk. >> >> It's "premature optimization" (look up the term) except for two cases: >> >> overnight runs and realtime 3D graphics. If your overnight run takes >> more >> >> than one night, you have a problem. If you're programming realtime 3D >> >> graphics and they're jerky, your users won't enjoy your simulation. But >> >> you wouldn't be using a SQL engine for 3D graphics anyway. >> >> >> >> The matters you mentioned were all worth attention back in the 1980s >> when >> >> storage and bandwidth were expensive. As you pointed out near the end >> of >> >> your post, these things matter less now. >> >> >> >> Simon. >> >> >> >> _______________________________________________ >> >> 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 >> _______________________________________________ >> 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 _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
