[ https://issues.apache.org/jira/browse/HIVE-1721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927545#action_12927545 ]
Namit Jain commented on HIVE-1721: ---------------------------------- T2 does not fit in memory completely. We create a bloom filter for T2, which fits in memory - the assumption here is that by filtering out a lot of rows from T1, we are reducing the number of rows that go to the reducer substantially, which helps the join performance > use bloom filters to improve the performance of joins > ----------------------------------------------------- > > Key: HIVE-1721 > URL: https://issues.apache.org/jira/browse/HIVE-1721 > Project: Hive > Issue Type: New Feature > Components: Query Processor > Reporter: Namit Jain > Assignee: Siying Dong > > In case of map-joins, it is likely that the big table will not find many > matching rows from the small table. > Currently, we perform a hash-map lookup for every row in the big table, which > can be pretty expensive. > It might be useful to try out a bloom-filter containing all the elements in > the small table. > Each element from the big table is first searched in the bloom filter, and > only in case of a positive match, > the small table hash table is explored. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.