Fragmentation: SQLite & Friends

I am happy to report that the SQLite fragmentation problem is now solved. I copied my profile a month ago, and my places.sqlite is still in a single fragment! There was a similar fix done to Firefox disk cache. Thanks to helpful comments on my OSX preallocation cry for help, we now preallocate efficiently on OSX too.

Startup cache is the last remaining bastion of fragmentation, but that’s already 10x better than it was a month ago. I have two complimentary solutions for that: either omnijar startup cache generation for core code and/or write the cache more efficiently.

Firefox 4 will be a lot more gentle on those spinning platters.

GCC

I helped Jan Hubicka on a GCC summit paper. Those nasty static initializers will not be a hassle in GCC 4.6!

I keep wanting to blog about how we switched to GCC 4.5 and how life is wonderful, but life didn’t work out this way. So far we tried switching away from 4.3 compiler three times. The first time GCC completely failed in terms of -Os performance. C++ -Os is more bloated in 4.5 (because that option is benchmarked on C apps). Then it turned out that libffi was being miscompiled (we also found a related bug in libffi). Last time, we tried switching to GCC 4.5 + -O3 since that performs much better than -Os, but that broke sunspider. Hopefully we can fix the sunspider issue and try again next week. I would really like to utilize GCC PGO to produce fastest possible Linux Firefox builds.

Nonetheless I happy with recent GCC progress. With Jan’s help, GCC will eventually be very good at compiling Mozilla. In my spare cycles I’ve been working on setting up GCC benchmarks using Mozilla to help avoid future surprises like we discovered in GCC 4.5. More on this later.