Sergei Golubchik <serg@xxxxxxxxxxxx> writes:
On Aug 17, Kristian Nielsen wrote:
Do you want to see the changes for when I implement async
commit_checkpoint_request() in InnoDB/XtraDB, before I push it to 10.0?
Yes, but it can be a separate patch.
Ok, will do.
"Controls the durability/speed trade-off for commits."
" Set to 0 (write and flush redo log to disk only once per second),"
" 1 (flush to disk at each commit),"
" 2 (write to kernel at commit but flush to disk only once per second)"
I find "write to kernel" very confusing.
May be "write to log" ?
Ok.
" or 3 (flush to disk twice per commit, usually redundant)."
I'd like "flush at prepare and at commit, usually redundant",
because otherwise one may ask why to flush twice at commit. It's easy to
overlook the prepare step and miss the difference between "twice PER
commit" and "twice AT commit" (especially as you write "AT commit"
above, for =1).
Ok. Thanks for the suggestions!
As you say, this should be easy. I need to store a list of cookies and their
associated LSN (not just a single cookie), but this is infrequently executed
so just a simple linked list with malloc/free of elements will work fine.
I thought you don't need a list. But simply
log_sys->cookie= cookie;
in innobase_checkpoint_request() and
if (log_sys->cookie)
{
ha_commit_checkpoint_notify(log_sys->cookie);
log_sys->cookie= 0;
}
in log_buffer_sync_in_background().
There can never be two cookies active, right?
Yes, there can. Why not?
Checkpointing is now asynchronous, there is nothing that prevents a new log
rotate and a new checkpoint request to happen before the old one finished. In
fact, this case is tested in binlog_checkpoint.test.
Of course in practise, this is unlikely to happen. It requires that the time
between binlog rotations is smaller than the time to complete a checkpoint.
We cannot call mark_xid_done() here, as we are holding LOCK_log - and
mark_xid_done() also takes (sometimes) LOCK_log.
Ok, so here you only decrement the counter, and mark_xid_done()
additionally might log a checkpoint event. It looks like it might sense
to extend mark_xid_done() with a second argument
-TC_LOG_BINLOG::mark_xid_done(ulong cookie)
+TC_LOG_BINLOG::mark_xid_done(ulong cookie, bool write_checkpoint)
then you'll be able to use it here and avoid code duplication.
Ok, done.
Thanks!
- Kristian.
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