← Back to team overview

maria-developers team mailing list archive

Re: can "set read_only" be non-blocking?


On Mon, Jun 27, 2011 at 8:24 AM, Michael Widenius <monty@xxxxxxxxxxxx>wrote:

> Hi!
> >>>>> "MARK" == MARK CALLAGHAN <mdcallag@xxxxxxxxx> writes:
> <cut>
> MARK> Can there be a variant that doesn't do #2? My workload doesn't use
> >> MyISAM
> MARK> and I don't know if #2 is done because of MyISAM. Calling
> MARK> close_cached_tables seems like a heavy way to force LOCK TABLEs to be
> MARK> unlocked. Any long running queries will cause #2 to block.
> >>
> >> The reason for 2 is to ensure that that all table info is written to
> >> disk so that if you do a snapshot or copy of tables, you will get
> >> things in a consistent state.
> >>
> >> This is mostly for MyISAM and non transactional tables, but it will
> >> also speed up things for InnoDB tables and allow you to copy xtradb
> >> tables from one server to another (if you are using table spaces)
> >> without having to take down the server.
> >>
> MARK> We are not using this for backup. This doesn't make it safe to copy
> MARK> InnoDB/XtraDB tables as the background IO threads can still do writes
> (flush
> MARK> dirty pages, merge insert buffer pages, purge delete rows.
> This is how innodb/xtradb works just now. However, I assume it should
> not be hard to fix XtraDB to flush things completely for tables that
> are closed and flushed and not in use by any transaction.
> (This is what Aria does today).
> >>
> >> It's possible to do a 'FLUSH TABLES FAST WITH READ LOCK' version that
> >> would only flush the header of MyISAM tables, which would probably
> >> help you, as long as you don't plan to copy any tables to any other
> >> server.
> >>
> >>
> MARK> We want a fast version of this to support other admin activities. In
> this
> MARK> case we don't care if this doesn't make it safe to backup MyISAM. Is
> it
> MARK> possible to provide that option and is it interesting for MariaDB to
> have
> MARK> such an option?
> What is possible relatively easy is to add the above FAST keyword to
> FLUSH TABLES.  For MyISAM tables it would do as I describe above, for
> other table type it would basicly be a nop and would thus solve your
> problem while being useful for others.
> I would expect this to something 8-16 hours of work.  Do you want me
> to do a worklog for this?

Assuming this won't block waiting for running queries to finish, yes let's
proceed with a worklog.

Mark Callaghan