[ https://issues.apache.org/jira/browse/HIVE-20977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16761064#comment-16761064 ]
Karthik Manamcheri commented on HIVE-20977: ------------------------------------------- Can we merge this [~pvary]? > 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 > Fix For: 4.0.0 > > Attachments: HIVE-20977.1.patch, HIVE-20977.2.patch, > HIVE-20977.3.patch, HIVE-20977.4.patch > > > 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. > -- This message was sent by Atlassian JIRA (v7.6.3#76005)