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https://issues.apache.org/jira/browse/HBASE-1192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12671960#action_12671960
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Erik Holstad commented on HBASE-1192:
-------------------------------------
In the instructions for SoftReferences you can find:
"All soft references to softly-reachable objects are guaranteed to have been
cleared before the virtual machine throws an OutOfMemoryError. Otherwise no
constraints are placed upon the time at which a soft reference will be cleared
or the order in which a set of such references to different objects will be
cleared. Virtual machine implementations are, however, encouraged to bias
against clearing recently-created or recently-used soft references."
Which would mean that the behavior would change from JVM to JVM, so the Lruness
of the system is clearly questionable.
Ran a test where I used SoftSortedValueMap and inserted 10M entries into it,
all entries were the same size.
i is the entry currently inserted
size of map before 1285540
size of deletes 1285537
size of map after 3
i 1285540
size of map before 1287469
size of deletes 443
size of map after 1287026
i 2573006
size of map before 1287027
size of deletes 2075
size of map after 1284952
i 2573007
size of map before 1284953
size of deletes 692
size of map after 1284261
i 2573008
size of map before 1284262
size of deletes 624
size of map after 1283638
i 2573009
size of map before 1283639
size of deletes 650
size of map after 1282989
i 2573010
size of map before 1282990
size of deletes 672
size of map after 1282318
i 2573011
size of map before 1282319
size of deletes 632
size of map after 1281687
i 2573012
size of map before 1281688
size of deletes 1281679
size of map after 9
i 2573013
size of map before 1285424
size of deletes 1285423
size of map after 1
i 3858428
size of map before 1286746
size of deletes 1286745
size of map after 1
i 5145173
size of map before 1285660
size of deletes 1285659
size of map after 1
i 6430832
size of map before 1286804
size of deletes 1286802
size of map after 2
i 7717635
size of map before 1286745
size of deletes 1286744
size of map after 1
i 9004378
So one can see that sometimes it evicts a some 100 entries for every insert and
other times
it basically empties the whole map, but waits long in between.
> LRU-style map for the block cache
> ---------------------------------
>
> Key: HBASE-1192
> URL: https://issues.apache.org/jira/browse/HBASE-1192
> Project: Hadoop HBase
> Issue Type: New Feature
> Components: regionserver
> Reporter: Jonathan Gray
> Priority: Blocker
> Fix For: 0.20.0
>
>
> We need to decide what structure to use to back the block cache. The primary
> decision is whether to continue using SoftReferences or to build our own
> structure.
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