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https://issues.apache.org/jira/browse/IMPALA-7501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16629621#comment-16629621
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Paul Rogers commented on IMPALA-7501:
-------------------------------------
So the above was probably looking in the wrong haystack. Todd's comment is the
key: {{LocalCatalog}}. The local catalog caches the HMS Thrift objects,
including {{Partition}}.
The chain is:
* {{LocalDb}} contains a map of {LocalTable}}.
* {{LocalTable}} has a subclass {{LocalFsTable}} which contains a map of
{{LocalPartitionSpec}} objects.
* {{LocalPartitionSpec}} has a relation (need to research) to
{{LocalFsPartition}}.
* {{LocalFsPartition}} holds onto the Hive {{Partition}}, which holds onto the
{{FieldSchema}} objects.
Short term, just need to track down how we cache the {{Partition}} and nuke the
{{FieldSchema}}, then retest.
Longer term, the note earlier does apply. While the query-specific metadata
goes to pains to avoid caching HMS objects, LocalCatalog (and presumably the
similar version in the {{catalogd}} do cache HMS objects which, as noted
earlier, are rather bloated for our needs.
> Slim down metastore Partition objects in LocalCatalog cache
> -----------------------------------------------------------
>
> Key: IMPALA-7501
> URL: https://issues.apache.org/jira/browse/IMPALA-7501
> Project: IMPALA
> Issue Type: Sub-task
> Reporter: Todd Lipcon
> Priority: Minor
>
> I took a heap dump of an impalad running in LocalCatalog mode with a 2G limit
> after running a production workload simulation for a couple hours. It had
> 38.5M objects and 2.02GB heap (the vast majority of the heap is, as expected,
> in the LocalCatalog cache). Of this total footprint, 1.78GB and 34.6M objects
> are retained by 'Partition' objects. Drilling into those, 1.29GB and 33.6M
> objects are retained by FieldSchema, which, as far as I remember, are ignored
> on the partition level by the Impala planner. So, with a bit of slimming down
> of these objects, we could make a huge dent in effective cache capacity given
> a fixed budget. Reducing object count should also have the effect of improved
> GC performance (old gen GC is more closely tied to object count than size)
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