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https://issues.apache.org/jira/browse/SOLR-665?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12617516#action_12617516
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funtick edited comment on SOLR-665 at 7/28/08 12:14 PM:
------------------------------------------------------------
Mark, thanks for going deeper. Yes, _resize_ may change ( Entry[ ] ) _table_,
_key_ will disappear from _bucket_ and _get() returns null:
{code}
/**
* The table, resized as necessary. Length MUST Always be a power of two.
*/
transient Entry[] table;
...
public V get(Object key) {
if (key == null)
return getForNullKey();
int hash = hash(key.hashCode());
for (Entry<K,V> e = table[indexFor(hash, table.length)];
e != null;
e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
return e.value;
}
return null;
}
{code}
Might get _null_ instead of MyValue (during _resize_ by another thread); not a
big deal! It is still Thread-Safe. Will add new entry (overwrite existing) in
such extremely rare cases.
- get() will _never_ return wrong value (Entry object is immutable in our case):
{code}
if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
return e.value;
{code}
was (Author: funtick):
Mark, thanks for going deeper. Yes, _resize_ may change ( Entry[ ] )
_table_, _key_ will disappear from _bucket_ and _get() returns null:
{code}
/**
* The table, resized as necessary. Length MUST Always be a power of two.
*/
transient Entry[] table;
...
public V get(Object key) {
if (key == null)
return getForNullKey();
int hash = hash(key.hashCode());
for (Entry<K,V> e = table[indexFor(hash, table.length)];
e != null;
e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
return e.value;
}
return null;
}
{code}
Might get _null_ instead of MyValue (during _resize_ by another thread); not a
big deal! It is still Thread-Safe. Will add new entry (overwrite existing) in
such extremely rare cases.
- get() will _never_ return wrong value (Entry object is immutable):
{code}
if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
return e.value;
{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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