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Posted to issues-all@impala.apache.org by "Li Penglin (Jira)" <ji...@apache.org> on 2023/01/06 11:05:00 UTC
[jira] [Assigned] (IMPALA-11802) Optimize count(*) queries for Iceberg V2 tables
[ https://issues.apache.org/jira/browse/IMPALA-11802?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Li Penglin reassigned IMPALA-11802:
-----------------------------------
Assignee: Li Penglin
> Optimize count(*) queries for Iceberg V2 tables
> -----------------------------------------------
>
> Key: IMPALA-11802
> URL: https://issues.apache.org/jira/browse/IMPALA-11802
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Reporter: Zoltán Borók-Nagy
> Assignee: Li Penglin
> Priority: Major
> Labels: impala-iceberg
>
> Simple {{SELECT count( * ) FROM ice_v2_tbl;}} could be optimized.
> At first we need to investigate if the following is true:
> If a V2 table only has position delete files, then the cardinality is
> {noformat}
> Cardinality(data files) - Cardinality(delete files)
> {noformat}
> If this is true, then we can answer count( * ) queries via a query rewrite similarly to what we do for V1 tables: IMPALA-11279
> If the above is not true, we can still optimize count( * ) queries by:
> {noformat}
> SUM
> |
> UNION ALL
> / \
> / \
> / \
> COUNT(*) COUNT(*)
> / \
> SCAN ANTI JOIN
> data files / \
> without / \
> deletes SCAN SCAN
> data files delete files
> with deletes
> {noformat}
> The SCAN operator with "data files without deletes" could benefit from count( * ) optimization (they would only need to read file metadata). In the common case (when there are few deletes) this SCAN is in charge of scanning the vast majority of data files.
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