Hi! Sorry it's taken a while to get back to you, I'm backed up after the conference last week (and vacation before that). I know on IRC I said to submit now, and that's good thing to do. Any comments below can simply be added as a comment to the proposal. We do read them!
Ajaya Agrawal <a9460509...@gmail.com> writes:
> Regarding the "improving replication policy in drizzle" I am writing a
> project proposal. I have talked to Stewart about this project over IRC
> channel.
>
>
> 1. This project's main goal is to implement a facility to wait for an
> event on a table.
> 2. The slave currently polls the master at regular intervals which is
> configurable, for replication events.If the above mentioned feature is
> implemented, instead of polling, we could send signals to slave regarding
> changes in replication log.
> 3. Finally we would make sure all the test cases still pass.
I'd add that it would also be useful for applications, which may also
use this feature instead of polling.
> *Implementation Overview:*
>
> 1. There is already a plugin for function interfaces in drizzle. We
> would use this interface to build our function interface which would wait
> for events on a specified table or database. The interface would be
> something like SELECT WAIT_FOR(INSERT, "local/test/table1"). This would
> wait for INSERT events on "table1" table and it would notify the slave of
> an insert event on the specified table. There is already an example of how
> to use function interface in plugin folder i.e. hello_world. I am currently
> trying to create an interface which would take arguments from an user
> looking at the above hello_world plugin.
> 2. There is already a plugin for monitoring the events in drizzled which
> is the event monitoring interface. There is also another plugin in
> drizzle/plugin/hello_events which waits for an event on a specified
> database or table which is specified in the command line while starting
> drizzled and prints to the console about the changes. We would use the
> event observer interface to create another interface which when
s/interface/function/
> given a
> table name or database name, notifies the observers of the changes
> happening. For e.g. this could be a slave which is interested in changes
> happening in the 'replication_log' table.
> 3. In part three of the project we would make sure all type of events on
> which a slave is interested is covered in our interface and all the test
> cases for slave still pass.
(after modifying the slave plugin)
> Am I required to produce some UML diagrams, use cases and design
> document?
No. A good outline like this is certainly a good start. You are not
*required* to create any UML diagrams/use cases, but they may help your
understanding of parts of the ssytem... and use cases are useful in
documenting the feature!
> I have not included the time out part because I couldn't understand the
> need of it. let's say there is this statement SELECT WAIT_FOR(INSERT,
> 'replication_log', 1). Does this mean that this would notify the slave of
> inserts which takes place within 1 second of issuing this statement?
Yes. This means you could, for example, easily then write a status
update to a table saying you're there looking and haven't just died (not
having traffic on a TCP connection can get you killed by things).
We should also construct an interface so that events are not missed.
e.g.
SELECT WAIT_FOR(INSERT, replication_log)
SELECT * FROM replication_log;
(another thread inserts something)
SELECT WAIT_FOR(INSERT, replication_log) <- would hang rather than
return instantly
Which could be as simple as returning an integer which is "number of
events observed." This means you could avoid the above like this:
SELECT WAIT_FOR(INSERT, replication_log, 0, 0)
Returns: 1
SELECT * FROM replication_log;
(another thread inserts something)
SELECT WAIT_FOR(INSERT, replication_log, 10, 1)
Returns: 2 (and instantly rather than waiting for 10 seconds as the
count is higher than the one passed in)
thoughts?
--
Stewart Smith
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