[infinispan-dev] CacheLoaders, Distribution mode and Interceptors

Tue Mar 19 12:25:18 EDT 2013

On 19 Mar 2013, at 14:12, Sanne Grinovero wrote:

> Mircea,
> what I was most looking forward was to you comment on the interceptor
> order generated for DIST+cachestores
> - we don't think the ClusteredCacheLoader should be needed at all
> - each DIST node is loading from the CacheLoader (any) rather than
> loading from its peer nodes for non-owned entries (!!)
My intention was to comment precisely on this matters, sorry if the comment wasn't clear enough :-)
I think you have fair point that the data should only be loaded from the cache store through the main owners: that's for correctness and performance reasons.
Naturally the ClusterCacheLoader would then be deprecated. Would you mind creating a JIRA for this?

> 
> This has come up on several threads now and I think it's critically
> wrong, as I commented previously this also introduces many
> inconsistencies - as far as I understand it.
> 
> BTW your gist wouldn't work, the metadata cache needs to load certain
> elements too. But nice you spotted the need to potentially filter what
> "preload" means in the scope of each cache, as the metadata one should
> only preload metadata, while in the original configuration this data
> would indeed be duplicated.
> Opened: https://issues.jboss.org/browse/ISPN-2938
> 
> Sanne
> 
> On 19 March 2013 11:51, Mircea Markus <mmarkus at redhat.com> wrote:
>> 
>> On 16 Mar 2013, at 01:19, Sanne Grinovero wrote:
>> 
>>> Hi Adrian,
>>> let's forget about Lucene details and focus on DIST.
>>> With numOwners=1 and having two nodes the entries should be stored
>>> roughly 50% on each node, I see nothing wrong with that
>>> considering you don't need data failover in a read-only use case
>>> having all the index available in the shared CacheLoader.
>>> 
>>> In such a scenario, and having both nodes preloaded all data, in case
>>> of a get() operation I would expect
>>> either:
>>> A) to be the owner, hence retrieve the value from local in-JVM reference
>>> B) to not be the owner, so to forward the request to the other node
>>> having roughly 50% chance per key to be in case A or B.
>>> 
>>> But when hitting case B) it seems that instead of loading from the
>>> other node, it hits the CacheLoader to fetch the value.
>>> 
>>> I already had asked James to verify with 4 nodes and numOwners=2, the
>>> result is the same so I suggested him to ask here;
>>> BTW I think numOwners=1 is perfectly valid and should work as with
>>> numOwners=1, the only reason I asked him to repeat
>>> the test is that we don't have much tests on the numOwners=1 case and
>>> I was assuming there might be some (wrong) assumptions
>>> affecting this.
>>> 
>>> Note that this is not "just" a critical performance problem but I'm
>>> also suspecting it could provide inconsistent reads, in two classes of
>>> problems:
>>> 
>>> # non-shared CacheStore with stale entries
>>> If for non-owned keys it will hit the local CacheStore first, where
>>> you might expect to not find anything, so to forward the request to
>>> the right node. What if this node has been the owner in the past? It
>>> might have an old entry locally stored, which would be returned
>>> instead of the correct value which is owned on a different node.
>>> 
>>> # shared CacheStore using write-behind
>>> When using an async CacheStore by definition the content of the
>>> CacheStore is not trustworthy if you don't check on the owner first
>>> for entries in memory.
>>> 
>>> Both seem critical to me, but the performance impact is really bad too.
>>> 
>>> I hoped to make some more tests myself but couldn't look at this yet,
>>> any help from the core team would be appreciated.
>> I think you have a fair point and reads/writes to the data should be coordinated through its owners both for performance and (more importantly) correctness.
>> Mind creating a JIRA for this?
>> 
>>> 
>>> @Ray, thanks for mentioning the ClusterCacheLoader. Wasn't there
>>> someone else with a CacheLoader issue recently who had worked around
>>> the problem by using a ClusterCacheLoader ?
>>> Do you remember what the scenario was?
>>> 
>>> Cheers,
>>> Sanne
>>> 
>>> On 15 March 2013 15:44, Adrian Nistor <anistor at redhat.com> wrote:
>>>> Hi James,
>>>> 
>>>> I'm not an expert on InfinispanDirectory but I've noticed in [1] that
>>>> the lucene-index cache is distributed with numOwners = 1. That means
>>>> each cache entry is owned by just one cluster node and there's nowhere
>>>> else to go in the cluster if the key is not available in local memory,
>>>> thus it needs fetching from the cache store. This can be solved with
>>>> numOwners > 1.
>>>> Please let me know if this solves your problem.
>>>> 
>>>> Cheers!
>>>> 
>>>> On 03/15/2013 05:03 PM, James Aley wrote:
>>>>> Hey all,
>>>>> 
>>>>> <OT>
>>>>> Seeing as this is my first post, I wanted to just quickly thank you
>>>>> all for Infinispan. So far I'm really enjoying working with it - great
>>>>> product!
>>>>> </OT>
>>>>> 
>>>>> I'm using the InfinispanDirectory for a Lucene project at the moment.
>>>>> We use Lucene directly to build a search product, which has high read
>>>>> requirements and likely very large indexes. I'm hoping to make use of
>>>>> a distribution mode cache to keep the whole index in memory across a
>>>>> cluster of machines (the index will be too big for one server).
>>>>> 
>>>>> The problem I'm having is that after loading a filesystem-based Lucene
>>>>> directory into InfinispanDirectory via LuceneCacheLoader, no nodes are
>>>>> retrieving data from the cluster - they instead look up keys in their
>>>>> local CacheLoaders, which involves lots of disk I/O and is very slow.
>>>>> I was hoping to just use the CacheLoader to initialize the caches, but
>>>>> from there on read only from RAM (and network, of course). Is this
>>>>> supported? Maybe I've misunderstood the purpose of the CacheLoader?
>>>>> 
>>>>> To explain my observations in a little more detail:
>>>>> * I start a cluster of two servers, using [1] as the cache config.
>>>>> Both have a local copy of the Lucene index that will be loaded into
>>>>> the InfinispanDirectory via the loader. This is a test configuration,
>>>>> where I've set numOwners=1 so that I only need two servers for
>>>>> distribution to happen.
>>>>> * Upon startup, things look good. I see the memory usage of the JVM
>>>>> reflect a pretty near 50/50 split of the data across both servers.
>>>>> Logging indicates both servers are in the cluster view, all seems
>>>>> fine.
>>>>> * When I send a search query to either one of the nodes, I notice the following:
>>>>>  - iotop shows huge (~100MB/s) disk I/O on that node alone from the
>>>>> JVM process.
>>>>>  - no change in network activity between nodes (~300b/s, same as when idle)
>>>>>  - memory usage on the node running the query increases dramatically,
>>>>> and stays higher even after the query is finished.
>>>>> 
>>>>> So it seemed to me like each node was favouring use of the CacheLoader
>>>>> to retrieve keys that are not in memory, instead of using the cluster.
>>>>> Does that seem reasonable? Is this the expected behaviour?
>>>>> 
>>>>> I started to investigate this by turning on trace logging, in this
>>>>> made me think perhaps the cause was that the CacheLoader's interceptor
>>>>> is higher priority in the chain than the the distribution interceptor?
>>>>> I'm not at all familiar with the design in any level of detail - just
>>>>> what I picked up in the last 24 hours from browsing the code, so I
>>>>> could easily be way off. I've attached the log snippets I thought
>>>>> relevant in [2].
>>>>> 
>>>>> Any advice offered much appreciated.
>>>>> Thanks!
>>>>> 
>>>>> James.
>>>>> 
>>>>> 
>>>>> [1] https://www.refheap.com/paste/12531
>>>>> [2] https://www.refheap.com/paste/12543
>>>>> _______________________________________________
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>>>>> infinispan-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>> 
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>> 
>> Cheers,
>> --
>> Mircea Markus
>> Infinispan lead (www.infinispan.org)
>> 
>> 
>> 
>> 
>> 
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Cheers,
-- 
Mircea Markus
Infinispan lead (www.infinispan.org)