2 Dec
2013
2 Dec
'13
10:36 a.m.
On 2 Dec 2013 at 10:26:33, vincent(a)massol.net
(vincent@massol.net(mailto://vincent@massol.net)) wrote:
[snip]
> > 1 - Document Cache Analysis
> > =======================
> >
> > * There are 3552 XWikiDocument in memory for 195MB
> > * The document cache size is 2000 on xwiki.org
> > * Large documents (such as Test Reports) take 6MB each (XDOM caching)
> > * So if we had only large documents in the wiki the cache would need
> > 2000*6MB = 12TO
> > * I don’t think this cache is memory aware, meaning it doesn’t free its
> > entries when memory is low
> > * 178MB for 2000 docs means average of 89K per document. Huge variation
> > between docs with big content and docs with no or small content
> >
> > This means that when memory is low on xwiki.org it should be enough to
> > call a few pages with some large content to get an OOM.
> >
> > 4 ideas to explore:
[snip]
I believe optimizing the XDOM memory footage is the
only real solution but we’ve already done a first pass on that and I don’t know much more
we can win. We should still have a second look and be creative ;)
For example, I’m sure we can find better ways for storing SpaceBlock, SymbolBlock, etc.
FTR:
* SpaceBlock (710035 instances): 22MB
* SpecialSymbolBlock (371857 instances): 14MB
* WordBlock (796535 instances): 79MB
* NewLinesBlock (25640): 820K
For example for storing just the letter “y” in a WordBlock, it takes 624 bytes vs 56 bytes
for the “y” in a String.
That’s because for we have parent refs, previous/next sibling refs, children blocks, param
blocks to save too.
Said differently, our current XDOM structure is not made to be memory efficient.
[snip]
Thanks
-Vincent
PS: The reason we use different instances for SpaceBlock and SpecialSymbolBlock ATM:
/**
* A new line block. Note that we don't make NewLineBlock a singleton since that
would cause problems when using
* Block APIs to manipulate a tree of blocks (for example to find the position of a
new line block in a list using
* {@link java.util.List#indexOf(Object)} wich would always return the first new line
block).
* @since 2.6RC1
*/