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Posted to issues-all@impala.apache.org by "Csaba Ringhofer (JIRA)" <ji...@apache.org> on 2019/05/15 14:19:00 UTC
[jira] [Commented] (IMPALA-6964) Track stats about column and page
sizes in Parquet reader
[ https://issues.apache.org/jira/browse/IMPALA-6964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16840447#comment-16840447 ]
Csaba Ringhofer commented on IMPALA-6964:
-----------------------------------------
I have not noticed during the implementation of IMPALA-6433 that only data pages are tracked, but not dictionary pages. The difference can be pretty large for string columns or if column indexes filter out most data pages.
> Track stats about column and page sizes in Parquet reader
> ---------------------------------------------------------
>
> Key: IMPALA-6964
> URL: https://issues.apache.org/jira/browse/IMPALA-6964
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Reporter: Tim Armstrong
> Assignee: Sahil Takiar
> Priority: Major
> Labels: observability, parquet, ramp-up
> Fix For: Impala 3.2.0
>
>
> It would be good to have stats for scanned parquet data about page sizes. We currently can't tell much about the "shape" of the parquet pages from the profile. Some questions that are interesting:
> * How big is each column? I.e. total compressed and decompressed size read.
> * How big are pages on average? Either compressed or decompressed size
> * What is the compression ratio for pages? Could be inferred from the above two.
> I think storing all the stats in the profile per-column would be too much data, but we could probably infer most useful things from higher-level aggregates.
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