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https://issues.apache.org/jira/browse/HIVE-20977?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Karthik Manamcheri reassigned HIVE-20977:
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> Lazy evaluate the table object in PreReadTableEvent to improve get_partition
> performance
> ----------------------------------------------------------------------------------------
>
> Key: HIVE-20977
> URL: https://issues.apache.org/jira/browse/HIVE-20977
> Project: Hive
> Issue Type: Improvement
> Reporter: Karthik Manamcheri
> Assignee: Karthik Manamcheri
> Priority: Minor
>
> The PreReadTableEvent is generated for non-table operations (such as
> get_partitions), but only if there is an event listener attached. However,
> this is also not necessary if the event listener is not interested in the
> read table event.
> For example, the TransactionalValidationListener's onEvent looks like this
> {code:java}
> @Override
> public void onEvent(PreEventContext context) throws MetaException,
> NoSuchObjectException,
> InvalidOperationException {
> switch (context.getEventType()) {
> case CREATE_TABLE:
> handle((PreCreateTableEvent) context);
> break;
> case ALTER_TABLE:
> handle((PreAlterTableEvent) context);
> break;
> default:
> //no validation required..
> }
> }{code}
>
> Note that for read table events it is a no-op. The problem is that the
> get_table is evaluated when creating the PreReadTableEvent finally to be just
> ignored!
> Look at the code below.. {{getMS().getTable(..)}} is evaluated irrespective
> of if the listener uses it or not.
> {code:java}
> private void fireReadTablePreEvent(String catName, String dbName, String
> tblName)
> throws MetaException, NoSuchObjectException {
> if(preListeners.size() > 0) {
> // do this only if there is a pre event listener registered (avoid
> unnecessary
> // metastore api call)
> Table t = getMS().getTable(catName, dbName, tblName);
> if (t == null) {
> throw new NoSuchObjectException(TableName.getQualified(catName, dbName,
> tblName)
> + " table not found");
> }
> firePreEvent(new PreReadTableEvent(t, this));
> }
> }
> {code}
> This can be improved by using a {{Supplier}} and lazily evaluating the table
> when needed (once when the first time it is called, memorized after that).
> *Motivation*
> Whenever a partition call occurs (get_partition, etc.), we fire the
> PreReadTableEvent. This affects performance since it fetches the table even
> if it is not being used. This change will improve performance on the
> get_partition calls.
>
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