[jira] [Commented] (SPARK-17994) Add back a file status cache for catalog tables

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-17994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15587106#comment-15587106 ] 

Apache Spark commented on SPARK-17994:
--------------------------------------

User 'ericl' has created a pull request for this issue:
https://github.com/apache/spark/pull/15539

> Add back a file status cache for catalog tables
> -----------------------------------------------
>
>                 Key: SPARK-17994
>                 URL: https://issues.apache.org/jira/browse/SPARK-17994
>             Project: Spark
>          Issue Type: Sub-task
>            Reporter: Eric Liang
>
> In SPARK-16980, we removed the full in-memory cache of table partitions in favor of loading only needed partitions from the metastore. This greatly improves the initial latency of queries that only read a small fraction of table partitions.
> However, since the metastore does not store file statistics, we need to discover those from remote storage. With the loss of the in-memory file status cache this has to happen on each query, increasing the latency of repeated queries over the same partitions.
> The proposal is to add back a per-table cache of partition contents, i.e. Map[Path, Array[FileStatus]]. This cache would be retained per-table, and can be invalidated through refreshTable() and refreshByPath(). Unlike the prior cache, it can be incrementally updated as new partitions are read.
> cc [~michael]



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