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From Michael Dürig <michael.due...@day.com>
Subject Re: jcr2spi NodeIterator.getNode() performances
Date Thu, 04 Mar 2010 13:30:59 GMT
> I am interested on these parameters to improve jackrabbit performance. I
> have an installation with more than 2 million of documents and performance
> is actually poor :(

On the current trunk there are 3 parameters which can be used to tweak 
performance for jcr2spi/spi2davex. These are the size of the item info 
cache, the size of the item cache and the depth of batch read operations.

Some Background:
The item cache contains JCR items (i.e. nodes and properties). The item 
info cache contains item infos. An item info is an entity representing 
nodes or properties on the SPI layer. The jcr2spi module receives item 
infos from an SPI implementation (i.e. spi2davex) and uses them to build 
up a hierarchy of JCR items.

When an item is requested from the JCR API, jcr2spi first checks whether 
the item is in the item cache. If so, that item is returned. If not, the 
request is passed down to the SPI. But before actually calling the SPI 
the item info cache is check first. If this cache contains the requested 
item info the relevant part of the JCR hierarchy is build and the 
corresponding JCR item is placed into the item cache. Only when the item 
info cache does not contain the requested item info a call will be made 
to the SPI. Here the batch read depth comes into play. Since calls to 
the SPI cause some latency (i.e. network round trips), the SPI may - in 
addition to the actually requested item info - return additional item 
infos. The batch read depth parameter specifies the depth down to which 
item infos of the children of the requested item info are returned.

Overall the size of the item info cache and the batch read depth should 
be used to optimize for the requirements of the back-end (i.e. network 
and server). In general, the item info cache should be large enough to 
*easily* hold all items from multiple batches. The batch read depth 
should be a trade off between network latency and item info cache 
overhead. Finally the item cache should be used to optimize for the 
requirements of the front-end (i.e. the JCR API client). It should be 
able to hold the items in the current working set of the API consumer.

Some pointers:

Batch reading: org.apache.jackrabbit.spi.RepositoryService#getItemInfos()

Item info cache size:

Item cache size:

Related JIRA issues:
JCR-2497: Improve jcr2spi read performance
JCR-2498: Implement caching mechanism for ItemInfo batches
JCR-2461: Item retrieval inefficient after refresh
JCR-2499: Add simple benchmarking tools for jcr2spi read perform


On 2/28/10 9:21 PM, Paco Avila wrote:
> El 28/02/2010 15:50, "Michael Dürig"<michael.duerig@day.com>  escribió:
> François,
> I spent some time on improving performance lately. See
> https://issues.apache.org/jira/browse/JCR-2497 and related issues.
> I was able to improve performance for our use case with these fixes. Getting
> the parameters right (i.e. item cache size, item info cache size and batch
> read depth) is still quite tricky though and requires careful profiling.
> I can provide more specific information on these parameters if required.
> Michael
> François Cassistat wrote:
>> Ok, I've studied a little what was going on with a packet analyze...

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