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https://issues.apache.org/jira/browse/HIVE-4051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13724818#comment-13724818
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Carl Steinbach commented on HIVE-4051:
--------------------------------------
{quote}
This introduces "direct SQL" optimization for metastore.
When memstore gets partitions by filter or by names, it does so using ANSI
SQL92 queries, if enabled (default).
This will not work on non-RDBMS datastores, may not work on non-ANSI-compiant
ones (I tested on mysql in default mode).
{quote}
Has anyone tested this patch on Derby, PostgreSQL, or Oracle? Until it's
verified to work on these DBs I think this new code should be disabled by
default.
> 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-4051.D11805.2.patch,
> HIVE-4051.D11805.3.patch, HIVE-4051.D11805.4.patch, HIVE-4051.D11805.5.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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