On 12/23/2005 4:57 AM, Florian G. Pflug wrote:
Jan Wieck wrote:
On 12/21/2005 8:18 PM, Florian G. Pflug wrote:
Florian G. Pflug wrote:
<snipped my own mail>
Can anyone confirm that this is actually a bug? I pretty sure
(Did multiple setups of my cluster, and the problem persisted -
I used the altperl scripts for setting up the cluster, so I
see no way I could have causes this).
If it's really I bug, I would at least be worth a note in
the docs or in the 1.1.5 release notes - I took me hours to
nail down the problem, and it wasn't fun, so preventing
others from having to do the same would be a good thing.
Rebuild listen entries is indeed broken. This is a show stopper for
1.1.5 ... I am working at it.
Is there a reason for not generating all "sensible" sl_listen entries?
I didn't find any documentation on the performance overhead a
sl_listen entry causes.
Exactly the "sensible" part of that all is important. Problems arise
when a node receives an event from any set-origin, which has not yet
been processed by its data provider for that set. For example
1 -> 2
3
1 being origin, 2 is subscriber, 3 is a new node not subscribed yet. 3
has paths for 1 and 2, so naturally it would listen on each of them for
their events. If we now subscribe 3 as a cascaded node with 2 as its
data provider, the ENABLE_SUBSCRIPTION event that will follow from node
1, on which node 3 will start copy_set, must be received by 3 from 2.
That is the only way that 2 at the moment where 3 starts to copy data
actually has data itself. It could still be busy with it's own copy_set,
meaning that not only the data in the tables is missing, the tables
themself aren't in sl_table either yet.
And to spice this up a little more, reading the events is done async in
the remote_listen thread. They are queued and the remote_worker thread
will process them from the queue. At the moment where node 3 gets the
SUBSCRIBE_SET event, it will have a lot of stuff already queued, so it
better restart ASAP to throw that away and listen again, this time for
all 1-events on 2.
Jan
With "sensible" I mean: Telling node X via sl_listen to ask neighbour-nodes
(Those for which a sl_path entry exists) for events from all other nodes,
apart from those for which the events must have travelled via node X to
reach the neighbour of X in question.
I tried writing an algorithm to do that, but it turned out that isn't quite
as easy as I initially believed, because all "iterative" algorithms
I could think off (Which were all based basically on the idea, that
if X receives events from Y, and Y from Z, then X can receive events from Z
via Y) failed because there is not enough information in sl_listen to figure
out if Y already needs X receive events from Z).
greetings, Florian Pflug
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