Reconsidering the default block cache size because of HFileV2

[Jean-Daniel Cryans <jd...@apache.org>]

Hey devs,

A thought just stuck me while I was writing down a more detailed block
caching documentation: with HFileV2, the indexes now live in the block
cache which means that those who upgrade may all of a sudden get
terrible cache hit ratios because of all that memory taken by the
indexes. This is somewhat mitigated by the fact that people don't
usually need to keep _all_ the index blocks in memory so in the end
we're more efficient.

Which brings me to a question: should we set hfile.block.cache.size
higher since indexes are now kept in the block cache? Currently it's
set to 20%.

Looking over my own production machines I see that the
storefileIndexSize is around 600-700MB so that's potentially how much
more data I'd have to block cache (more likely it's half of that
that's really being used actively).

What would be a good new default? 25%? 30%? How do we handle those
that will be pushed over the BC+memstore size limit because of that
change?

Thx,

J-D

Re: Reconsidering the default block cache size because of HFileV2

[Jean-Daniel Cryans <jd...@apache.org>]

Silence means yes, so I'll open a jira and bump that to 25%.

J-D

On Mon, Dec 12, 2011 at 5:47 PM, Jean-Daniel Cryans <jd...@apache.org> wrote:
> Hey devs,
>
> A thought just stuck me while I was writing down a more detailed block
> caching documentation: with HFileV2, the indexes now live in the block
> cache which means that those who upgrade may all of a sudden get
> terrible cache hit ratios because of all that memory taken by the
> indexes. This is somewhat mitigated by the fact that people don't
> usually need to keep _all_ the index blocks in memory so in the end
> we're more efficient.
>
> Which brings me to a question: should we set hfile.block.cache.size
> higher since indexes are now kept in the block cache? Currently it's
> set to 20%.
>
> Looking over my own production machines I see that the
> storefileIndexSize is around 600-700MB so that's potentially how much
> more data I'd have to block cache (more likely it's half of that
> that's really being used actively).
>
> What would be a good new default? 25%? 30%? How do we handle those
> that will be pushed over the BC+memstore size limit because of that
> change?
>
> Thx,
>
> J-D