[jira] [Created] (KUDU-3197) Tablet keeps all history schemas in memory may result in high memory consumption

["wangningito (Jira)" <ji...@apache.org>]

wangningito created KUDU-3197:
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             Summary: Tablet keeps all history schemas in memory may result in high memory consumption
                 Key: KUDU-3197
                 URL: https://issues.apache.org/jira/browse/KUDU-3197
             Project: Kudu
          Issue Type: Improvement
          Components: tablet
    Affects Versions: 1.13.0
            Reporter: wangningito
            Assignee: wangningito
         Attachments: image-2020-09-25-14-45-33-402.png, image-2020-09-25-14-49-30-913.png, image-2020-09-25-15-05-44-948.png

In case of high frequency of updating table, memory consumption of kudu-tserver may be very high, and the memory in not tracked in the memory page. 

This is the memory usage of a tablet, the memory consumption of tablet-xxx‘s peak is 3.6G， but none of its' childrens' memory can reach.

!image-2020-09-25-14-45-33-402.png!

So I use pprof to get the heap sampling. The tserver started for long but the memory is still consuming by TabletBootstrap:PlayAlterSchemaRequest. 

!image-2020-09-25-14-49-30-913.png!

I change the `old_schemas_` in tablet_metadata.h to a fixed size vector, 

    // Previous values of 'schema_'.
    // These are currently kept alive forever, under the assumption that
    // a given tablet won't have thousands of "alter table" calls.
    // They are kept alive so that callers of schema() don't need to
    // worry about reference counting or locking.
    std::vector<Schema*> old_schemas_;

The heap sampling then becomes
 !image-2020-09-25-15-05-44-948.png! 

So, to make application layer more flexible, it could be better to make the size of the old_schemas configurable.
 



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