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https://issues.apache.org/jira/browse/CASSANDRA-7438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14231878#comment-14231878
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Vijay edited comment on CASSANDRA-7438 at 12/2/14 8:31 PM:
-----------------------------------------------------------
EDIT:
Here is the explanation. run the benchmark with the following options (lruc
benchmark).
{code}java -Djava.library.path=/usr/local/lib/ -jar ~/lrucTest.jar -t 30 -s
6147483648 -c ohc{code}
And you will see something like this (errors == not found from the cache even
though you have all the items you need is in the cache).
{code}
Memory consumed: 3 GB / 5 GB or 4288887170 / 6147483648, size 49999980, queued
(LRU q size) 0
VM total:2 GB
VM free:2 GB
Get Operation (micros)
time_taken, count, mean, median, 99thPercentile, 999thPercentile, error
4734724, 1666666, 2.42, 1.93, 8.58, 24.74, 1666666
4804375, 1666666, 2.40, 1.92, 4.56, 106.23, 1666666
4805858, 1666666, 2.45, 1.95, 3.94, 11.76, 1666666
4842886, 1666666, 2.40, 1.92, 7.46, 26.73, 1666666
{code}
You really need test cases :)
Anyways i am going to stop working on this ticket now, let me know if someone
wants any other info.
was (Author: [email protected]):
Never mind, my bad it was related the below (which needs to be more
configurable instead) and the items where going missing earlier than i thought
it should and looks you just evict the items per segment (If a segment is used
more more items will disappear from that segment and the lest used segment
items will remain).
{code}
// 12.5% if capacity less than 8GB
// 10% if capacity less than 16 GB
// 5% if capacity is higher than 16GB
{code}
Also noticed you don't have replace which Cassandra uses.
Anyways i am going to stop working on this for now, let me know if someone
wants any other info.
> Serializing Row cache alternative (Fully off heap)
> --------------------------------------------------
>
> Key: CASSANDRA-7438
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7438
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Environment: Linux
> Reporter: Vijay
> Assignee: Vijay
> Labels: performance
> Fix For: 3.0
>
> Attachments: 0001-CASSANDRA-7438.patch, tests.zip
>
>
> Currently SerializingCache is partially off heap, keys are still stored in
> JVM heap as BB,
> * There is a higher GC costs for a reasonably big cache.
> * Some users have used the row cache efficiently in production for better
> results, but this requires careful tunning.
> * Overhead in Memory for the cache entries are relatively high.
> So the proposal for this ticket is to move the LRU cache logic completely off
> heap and use JNI to interact with cache. We might want to ensure that the new
> implementation match the existing API's (ICache), and the implementation
> needs to have safe memory access, low overhead in memory and less memcpy's
> (As much as possible).
> We might also want to make this cache configurable.
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