On Mon, Oct 21, 2019 at 10:31 AM Richard Hipp <d...@sqlite.org> wrote: > > On 10/21/19, Jonathan Brandmeyer <jbrandme...@planetiq.com> wrote: > > Or, how many times is each page written by SQLite for an insert-heavy > > test? The answer appears to be "4", but I can only account for two of > > those four. > > Are you measuring writes at the OS-interface layer, or writes at the > hardware layer? SQLite should issue no more than 2x writes in WAL > mode, and less if the same page is modified more than once. But who > knows how the OS might be multiplying this to accomplish its own > filesystem consistency. > > Consider compiling the > https://www.sqlite.org/src/file/ext/misc/vfslog.c extension into > SQLite on a workstation and running your code there, to get more > details about everything that SQLite is doing with storage.
Thanks for the pointer. I didn't do this exactly, but instead instrumented SQLite's unixWrite() and my lowest-level NAND driver's block write function on the target hardware to capture summary counters of both events. The filesystem's own consistency overhead adds up to about 2% additional writes - not nearly enough to account for the missing 2x. The throughput implied by the low-level counters is consistent with the benchmark results. Thanks, -- Jonathan Brandmeyer PlanetiQ _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
