如何调整配置单元以查询元数据？

Question

In case I am running a below hive query on table with certain partitioned column, I want to make sure hive does not do full table scan and just figure out the result from meta data itself. Is there any way to enable this ?

Select max(partitioned_col) from hive_table ;

Right now , when I am running this query , its launching map reduce tasks and I am sure its doing data scan while it can very well figure out the value from metadata itself.

Answer 1

Compute table statistics every time you changed data.

ANALYZE TABLE hive_table PARTITION(partitioned_col) COMPUTE STATISTICS FOR COLUMNS;

Enable CBO and statistics auto gathering:

set hive.cbo.enable=true;
set hive.stats.autogather=true;

Use these settings to enable CBO using statistics:

set hive.compute.query.using.stats=true;
set hive.stats.fetch.partition.stats=true;
set hive.stats.fetch.column.stats=true;

If nothing helps I'd recommend to apply this approach for finding last partition fast: Parse max partition key using shell script from the table location. The command below will print all table folder paths, sort, take latest sorted, take last subfolder name, parse partition folder name and extract value. All you need is to initialize TABLE_DIR variable and put the number of partition subfolder in the path :

last_partition=$(hadoop fs -ls $TABLE_DIR/* | awk '{ print $8 }' | sort -r | head -n1 | cut -d / -f [number of partition subfolder in the path here] | cut -d = -f 2

Then use $last_partition variable to pass to your script as

  hive -hiveconf last_partition="$last_partition" -f your_script.hql