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https://issues.apache.org/jira/browse/HIVE-4051?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sergey Shelukhin updated HIVE-4051:
-----------------------------------
Status: Patch Available (was: Open)
> Hive's metastore suffers from 1+N queries when querying partitions & is slow
> ----------------------------------------------------------------------------
>
> Key: HIVE-4051
> URL: https://issues.apache.org/jira/browse/HIVE-4051
> Project: Hive
> Issue Type: Bug
> Components: Clients, Metastore
> Environment: RHEL 6.3 / EC2 C1.XL
> Reporter: Gopal V
> Assignee: Sergey Shelukhin
> Attachments: HIVE-4051.D11805.1.patch
>
>
> Hive's query client takes a long time to initialize & start planning queries
> because of delays in creating all the MTable/MPartition objects.
> For a hive db with 1800 partitions, the metastore took 6-7 seconds to
> initialize - firing approximately 5900 queries to the mysql database.
> Several of those queries fetch exactly one row to create a single object on
> the client.
> The following 12 queries were repeated for each partition, generating a storm
> of SQL queries
> {code}
> 4 Query SELECT
> `A0`.`SD_ID`,`B0`.`INPUT_FORMAT`,`B0`.`IS_COMPRESSED`,`B0`.`IS_STOREDASSUBDIRECTORIES`,`B0`.`LOCATION`,`B0`.`NUM_BUCKETS`,`B0`.`OUTPUT_FORMAT`,`B0`.`SD_ID`
> FROM `PARTITIONS` `A0` LEFT OUTER JOIN `SDS` `B0` ON `A0`.`SD_ID` =
> `B0`.`SD_ID` WHERE `A0`.`PART_ID` = 3945
> 4 Query SELECT `A0`.`CD_ID`,`B0`.`CD_ID` FROM `SDS` `A0` LEFT OUTER JOIN
> `CDS` `B0` ON `A0`.`CD_ID` = `B0`.`CD_ID` WHERE `A0`.`SD_ID` =4871
> 4 Query SELECT COUNT(*) FROM `COLUMNS_V2` THIS WHERE THIS.`CD_ID`=1546
> AND THIS.`INTEGER_IDX`>=0
> 4 Query SELECT
> `A0`.`COMMENT`,`A0`.`COLUMN_NAME`,`A0`.`TYPE_NAME`,`A0`.`INTEGER_IDX` AS
> NUCORDER0 FROM `COLUMNS_V2` `A0` WHERE `A0`.`CD_ID` = 1546 AND
> `A0`.`INTEGER_IDX` >= 0 ORDER BY NUCORDER0
> 4 Query SELECT `A0`.`SERDE_ID`,`B0`.`NAME`,`B0`.`SLIB`,`B0`.`SERDE_ID`
> FROM `SDS` `A0` LEFT OUTER JOIN `SERDES` `B0` ON `A0`.`SERDE_ID` =
> `B0`.`SERDE_ID` WHERE `A0`.`SD_ID` =4871
> 4 Query SELECT COUNT(*) FROM `SORT_COLS` THIS WHERE THIS.`SD_ID`=4871 AND
> THIS.`INTEGER_IDX`>=0
> 4 Query SELECT `A0`.`COLUMN_NAME`,`A0`.`ORDER`,`A0`.`INTEGER_IDX` AS
> NUCORDER0 FROM `SORT_COLS` `A0` WHERE `A0`.`SD_ID` =4871 AND
> `A0`.`INTEGER_IDX` >= 0 ORDER BY NUCORDER0
> 4 Query SELECT COUNT(*) FROM `SKEWED_VALUES` THIS WHERE
> THIS.`SD_ID_OID`=4871 AND THIS.`INTEGER_IDX`>=0
> 4 Query SELECT 'org.apache.hadoop.hive.metastore.model.MStringList' AS
> NUCLEUS_TYPE,`A1`.`STRING_LIST_ID`,`A0`.`INTEGER_IDX` AS NUCORDER0 FROM
> `SKEWED_VALUES` `A0` INNER JOIN `SKEWED_STRING_LIST` `A1` ON
> `A0`.`STRING_LIST_ID_EID` = `A1`.`STRING_LIST_ID` WHERE `A0`.`SD_ID_OID`
> =4871 AND `A0`.`INTEGER_IDX` >= 0 ORDER BY NUCORDER0
> 4 Query SELECT COUNT(*) FROM `SKEWED_COL_VALUE_LOC_MAP` WHERE `SD_ID`
> =4871 AND `STRING_LIST_ID_KID` IS NOT NULL
> 4 Query SELECT 'org.apache.hadoop.hive.metastore.model.MStringList' AS
> NUCLEUS_TYPE,`A0`.`STRING_LIST_ID` FROM `SKEWED_STRING_LIST` `A0` INNER JOIN
> `SKEWED_COL_VALUE_LOC_MAP` `B0` ON `A0`.`STRING_LIST_ID` =
> `B0`.`STRING_LIST_ID_KID` WHERE `B0`.`SD_ID` =4871
> 4 Query SELECT `A0`.`STRING_LIST_ID_KID`,`A0`.`LOCATION` FROM
> `SKEWED_COL_VALUE_LOC_MAP` `A0` WHERE `A0`.`SD_ID` =4871 AND NOT
> (`A0`.`STRING_LIST_ID_KID` IS NULL)
> {code}
> This data is not detached or cached, so this operation is performed during
> every query plan for the partitions, even in the same hive client.
> The queries are automatically generated by JDO/DataNucleus which makes it
> nearly impossible to rewrite it into a single denormalized join operation &
> process it locally.
> Attempts to optimize this with JDO fetch-groups did not bear fruit in
> improving the query count.
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