cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "James Golick (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1214) Make standard IO the default
Date Tue, 22 Jun 2010 15:23:56 GMT


James Golick commented on CASSANDRA-1214:

I have tried many levels of swappiness (including 0) without any change in behaviour. Additionally,
I haven't seen much if any change in performance with standard IO.

Continuing to iterate on the mmap code might be a good idea. But, it's the wrong default.
Especially now that we've agreed that it is currently broken. It's possible that it may be
a sensible default in the future, but right now, it's not a good choice for production (in
most cases).

> Make standard IO the default
> ----------------------------
>                 Key: CASSANDRA-1214
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 0.7
>            Reporter: James Golick
> The way mmap()'d IO is handled in cassandra is dangerous. It allocates potentially massive
buffers without any care for bounding the total size of the program's buffers. As the node's
dataset grows, this *will* lead to swapping and instability.
> This is a dangerous and wrong default for a couple of reasons.
> 1) People are likely to test cassandra with the default settings. This issue is insidious
because it only appears when you have sufficient data in a certain node, there is absolutely
no way to control it, and it doesn't at all respect the memory limits that you give to the
> That can all be ascertained by reading the code, and people should certainly do their
homework, but nevertheless, cassandra should ship with sane defaults that don't break down
when you cross some magic unknown threshold.
> 2) It's deceptive. Unless you are extremely careful with capacity planning, you will
get bit by this. Most people won't really be able to use this in production, so why get them
excited about performance that they can't actually have?

This message is automatically generated by JIRA.
You can reply to this email to add a comment to the issue online.

View raw message