incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Jonathan Ellis <jbel...@gmail.com>
Subject Re: on bootstrapping a node
Date Wed, 28 Oct 2009 05:02:47 GMT
On Tue, Oct 27, 2009 at 10:10 PM, Edmond Lau <edmond@ooyala.com> wrote:
> I'd like to improve my mental model of how Cassandra bootstrapping
> works.  My understanding is that bootstrapping is just an extra step
> during a node's startup where the node copies data from neighboring
> nodes that, according to its token, it should own; afterwards, the
> node behaves like any other node.
>
> If that's correct, I have a few follow-up questions:
>
> - At what point does the new node get inserted into the hash ring so
> that reads/writes for keys get directed to it?

It starts accepting reads when bootstrap is complete, but during
bootstrap it will also be forwarded writes so it stays up-to-date.

> - What are the semantics of bootstrapping a node that's been in the
> cluster before and already has some data that's possibly outdated?
> Should this work?  This might be useful if a node's been out of
> commission for sufficiently long period of time.

Cluster membership is intended to be relatively stable.  When removing
nodes is supported (see
https://issues.apache.org/jira/browse/CASSANDRA-435), it won't be
worth special-casing the case of "new node, that has some data locally
that is arbitrarily out of date."  So you will want to wipe its data
directories and re-bootstrap it.

> - If we pick a poor set of initial tokens, would it be sensible to
> modify the tokens on existing nodes and then restart them with
> bootstrapping in order to rebalance?

Not until https://issues.apache.org/jira/browse/CASSANDRA-193 is done
so you can fix the damage you've done to your replicas.

> I've also noticed that I can get my cassandra cluster into a weird
> state via bootstrapping, where it stops accepting reads/writes.  I'm
> on Cassandra 0.4.1.  A simple repro case is to start all 3 nodes of a
> 3 node cluster (replication factor of 2) using bootstrapping.  Getting
> a key that I've inserted then leads to an IndexOutOfBoundsException.
> Another IndexOutOfBoundsException was thrown later while flushing.

Starting all nodes in bootstrap mode is not a supported operation.
Don't do that.  (Bootstrap is much more automatic in trunk, and fixes
this specific problem as well as others.)

-Jonathan

Mime
View raw message