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https://issues.apache.org/jira/browse/SOLR-665?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12617549#action_12617549
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Mike Klaas commented on SOLR-665:
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[quote]We may simply use java.util.concurrent.locks instead of heavy
synchronized... we may also use Executor framework instead of single-thread
faceting... We may even base SOLR on Apache MINA project.[/quote]
Simply replacing synchronized with java.util.concurrent.locks doesn't increase
performance. There needs to be a specific strategy for employing these locks
in a way that makes sense.
For instance, one idea would be to create a read/write lock with the put()'s
covered by write and get()'s covered by read. This would allow multiple
parallel reads and will be thread-safe. Another is to create something like
ConcurrentLinkedHashMap.
These strategies should be tested before trying to create a lock-free get()
version, which if even possible, would rely deeply on the implementation (such
a structure would have to be created from scratch, I believe). I'd expect
anyone that is able to create such a thing be familiar enough wiht memory
barriers and such issues to be able to deeply explain the problems with
double-checked locking off the top of their head (and immediately see such
problems in other code)
> FIFO Cache (Unsynchronized): 9x times performance boost
> -------------------------------------------------------
>
> Key: SOLR-665
> URL: https://issues.apache.org/jira/browse/SOLR-665
> Project: Solr
> Issue Type: Improvement
> Affects Versions: 1.3
> Environment: JRockit R27 (Java 6)
> Reporter: Fuad Efendi
> Attachments: FIFOCache.java
>
> Original Estimate: 672h
> Remaining Estimate: 672h
>
> Attached is modified version of LRUCache where
> 1. map = new LinkedHashMap(initialSize, 0.75f, false) - so that
> "reordering"/true (performance bottleneck of LRU) is replaced to
> "insertion-order"/false (so that it became FIFO)
> 2. Almost all (absolutely unneccessary) synchronized statements commented out
> See discussion at
> http://www.nabble.com/LRUCache---synchronized%21--td16439831.html
> Performance metrics (taken from SOLR Admin):
> LRU
> Requests: 7638
> Average Time-Per-Request: 15300
> Average Request-per-Second: 0.06
> FIFO:
> Requests: 3355
> Average Time-Per-Request: 1610
> Average Request-per-Second: 0.11
> Performance increased 9 times which roughly corresponds to a number of CPU in
> a system, http://www.tokenizer.org/ (Shopping Search Engine at Tokenizer.org)
> Current number of documents: 7494689
> name: filterCache
> class: org.apache.solr.search.LRUCache
> version: 1.0
> description: LRU Cache(maxSize=10000000, initialSize=1000)
> stats: lookups : 15966954582
> hits : 16391851546
> hitratio : 0.102
> inserts : 4246120
> evictions : 0
> size : 2668705
> cumulative_lookups : 16415839763
> cumulative_hits : 16411608101
> cumulative_hitratio : 0.99
> cumulative_inserts : 4246246
> cumulative_evictions : 0
> Thanks
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