On 05/12/2012 1:25 PM, Dan Kennedy wrote:
On 12/06/2012 12:47 AM, Black, Michael (IS) wrote:
I'm a bit confused with "always aligned". None of the lseeks in this
log are 1024 aligned.
And I just ran a test with the 3.7.15.1 latest amalgamation and most
of these seeks are not aligned. Once in a while it gets lucky.
Alignment sure isn't deliberate in this. It appears the first page
is 1080 which is already out of alignment. File#4 here is the wal
file.
I wasn't clear. Writes to the WAL file are not aligned. However,
they are usually sequential, which means on an OS with a smart
enough cache you don't really gain anything at all trying to align
them.
That hypothesis could be easily tested by examining the corresponding
strace output for mysql... I don't know if sqlite3's unaligned log
writes are actually slow (didn't see this info in any of Keith's
messages), but if they are that would suggest the hypothesis is false;
it would really put nails in the coffin if mysql uses aligned log writes.
(BTW Michael, whatever mechanism you use to reply breaks threading in
both Thunderbird and the list archives at sqlite.org; makes it harder to
follow conversations)
Ryan
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