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https://issues.apache.org/jira/browse/IMPALA-11293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17682942#comment-17682942
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Li Penglin commented on IMPALA-11293:
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Actually, maybe users don't want to compact the entire table, that may be a
long wait, they prefer partition-level compactions. I briefly listed my
half-baked ideas:
1. Create a temporary Iceberg table with the 'CREATE TABLE AS SELECT * from
ice_tbl where partition_cols ...' statement(We need to make a note of the
snapshotid, which we'll use in step.3 to know which files we're replacing).
2. Move the data from the temporary iceberg table to the partition directory of
the target table, these files are used to replace the smaller files.
3. Submit a RewriteFiles commit using Iceberg API:
https://github.com/apache/iceberg/blob/master/api/src/main/java/org/apache/iceberg/Table.java#L233.
4. Clean the temporary Iceberg table.
> Add COMPACT command for Iceberg tables
> --------------------------------------
>
> Key: IMPALA-11293
> URL: https://issues.apache.org/jira/browse/IMPALA-11293
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Reporter: Zoltán Borók-Nagy
> Assignee: Tamas Mate
> Priority: Major
> Labels: impala-iceberg
>
> Currently Impala cannot compact Iceberg tables.
> The following INSERT OVERWRITE statement could be used in the simple cases,
> i.e. when the following conditions meet:
> * all data files use the same partition spec (i.e. no partition evolution)
> * no bucket partitioning (we currently forbid INSERT OVERWRITE for bucket
> partitioning)
> {noformat}
> INSERT OVERWRITE t SELECT * FROM t;{noformat}
> We could have a command that compacts the Iceberg table (syntax needs to be
> the same with Hive), e.g.:
> {noformat}
> ALTER TABLE t EXECUTE compaction();{noformat}
> At first, the compact command could be just rewritten to the INSERT OVERWRITE
> command, but it would also check that there's no partition evolution.
> The "no bucket" partitioning condition could be relaxed in this case, because
> the result would be deterministic. I.e. the only condition we need to check
> is that there was no partition evolution.
> Later, we could do compaction by
> {noformat}
> TRUNCATE TABLE t;
> INSERT INTO t SELECT * FROM t FOR SYSTEM_TIME AS OF ...;{noformat}
> Currently time-travel queries are not optimized, but we could workaround it
> by doing planning at first of:
> {noformat}
> Create the plan for:
> TRUNCATE TABLE t;
> INSERT INTO t SELECT * FROM t;{noformat}
> Then execute them:
> {noformat}
> Actually execute:
> TRUNCATE TABLE t;
> INSERT INTO t SELECT * FROM t; (no need for time-travel, plan was created
> before TRUNCATE){noformat}
> This could workaround the planning overhead of time-travel queries.
> Also, we might add some locking for the table if possible.
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