[jira] [Commented] (HIVE-15367) CTAS with LOCATION should write temp data under location directory rather than database location

["Sahil Takiar (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-15367?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15724008#comment-15724008 ] 

Sahil Takiar commented on HIVE-15367:
-------------------------------------

[~spena], [~ychena] you were looking at this logic as part of HIVE-11427, any chance you could comment on if my logic sounds correct?

> CTAS with LOCATION should write temp data under location directory rather than database location
> ------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-15367
>                 URL: https://issues.apache.org/jira/browse/HIVE-15367
>             Project: Hive
>          Issue Type: Bug
>          Components: Hive
>            Reporter: Sahil Takiar
>            Assignee: Sahil Takiar
>
> For regular CTAS queries, temp data from a SELECT query will be written to to a staging directory under the database location. The code to control this is in {{SemanticAnalyzer.java}}
> {code}
>              // allocate a temporary output dir on the location of the table
>               String tableName = getUnescapedName((ASTNode) ast.getChild(0));
>               String[] names = Utilities.getDbTableName(tableName);
>               Path location;
>               try {
>                 Warehouse wh = new Warehouse(conf);
>                 //Use destination table's db location.
>                 String destTableDb = qb.getTableDesc() != null? qb.getTableDesc().getDatabaseName(): null;
>                 if (destTableDb == null) {
>                   destTableDb = names[0];
>                 }
>                 location = wh.getDatabasePath(db.getDatabase(destTableDb));
>               } catch (MetaException e) {
>                 throw new SemanticException(e);
>               }
> {code}
> However, CTAS queries allow specifying a {{LOCATION}} for the new table. Its possible for this location to be on a different filesystem than the database location. If this happens temp data will be written to the database filesystem and will be copied to the table filesystem in {{MoveTask}}.
> This extra copying of data can drastically affect performance. Rather than always use the database location as the staging dir for CTAS queries, Hive should first check if there is an explicit {{LOCATION}} specified in the CTAS query. If there is, staging data should be stored under the {{LOCATION}} directory.



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