Is it possible to see the total number of partitions of a table in impala?
For example db.table has 40.500 partitions
Use SHOW PARTITIONS statement.
SHOW PARTITIONS [database_name.]table_name
It will print partition list and you can count rows in the output minus header(3 rows) and footer(1 row). Unfortunately, there is no command which can return partition count already calculated except for Kudu tables: SHOW TABLE STATS prints the # of partitions in Kudu table.
Of course you can execute select count(distinct part_col1, part_col2...) from table, but it is not as efficient as SHOW partitions
Related
I applied a partition on a DateTime column in a MSSQL table .
Created Partition function, Scheme and 4 file groups and given boundary values.
I have queried a result in this table with where condition on partitioned column.
In this how-to know, the query is reading total records or related filegroup.
How to know the query is using partition or not ?.
One way is with the actual query execution plan. The Actual Partition Count of the seek/scan operator will show the actual number of partitions touched.
Another method is to run the query with SET STATISTICS IO ON, where the scan count of the table will reflect the number of partitions used.
I've recently moved to using AvroSerDe for my External tables in Hive.
Select col_name,count(*)
from table
group by col_name;
The above query gives me a count. Where as the below query does not:
Select count(*)
from table;
The reason is hive just looks at the table metadata and fetches the values. For some reason, statistics for the table is not updated in hive due to which count(*) returns 0.
The statistics is written with no data rows at the time of table creation and for any data appends/changes, hive requires to update this statistics in the metadata.
Running ANALYZE command gather statistics and write them into Hive MetaStore.
ANALYZE TABLE table_name COMPUTE STATISTICS;
Visit Apache Hive wiki for more details about ANALYZE command.
Other methods to solve this issue
Use of 'limit' and 'group by' clause triggers map reduce job to get
the count of number of rows and gives correct value
Setting fetch task conversion to none forces hive to run a map reduce
job to count the number of rows
hive> set hive.fetch.task.conversion=none;
Is there any way to limit the number of Hive partitions while listing the partitions in show command?
I have a Hive table which has around 500 partitions and I wanted the latest partition alone. The show command list all the partitions. I am using this partition to find out the location details. I do not have access to metastore to query the details and the partition location is where the actual data resides.
I tried set hive.limit.query.max.table.partition=1 but this does not affect the metastore query. So, is there any other way to limit the partitions listed?
Thank you,
Revathy.
Are you running from the command line?
If so you can get your desired with something like this:
hive -e "set hive.cli.print.header=false;show partitions table_name;" | tail -1
There is a "BAD" way to obtain what you want. You can treat the partitions columns like other columns and extract them into a select with limit query:
SELECT DISTINCT partition_column
FROM partitioned_table
ORDER BY partition_column
LIMIT 1;
The only way to filter a SHOW PARTION is using PARTITION:
SHOW PARTITIONS partitioned_table PARTION ( partitioned_column = "somevalue" );
Is there a way of getting a list of the partitions in a BigQuery date-partitioned table? Right now the best way I have found of do this is using the _PARTITIONTIME meta-column, but this needs to scan all the rows in all the partitions. Is there an equivalent to a show partitions call or maybe something in the bq command-line tool?
To list partitions in a table, query the table's summary partition by using the partition decorator separator ($) followed by PARTITIONS_SUMMARY. For example, the following command retrieves the partition IDs for table1:
SELECT partition_id from [mydataset.table1$__PARTITIONS_SUMMARY__];
My table have 7 million records and I do split table in 14 part according to ID, each partition include 5 million record and size of partition is 40G. I want to run a query to get count in one partition but it scan all partitions and time of Query become very large.
SELECT COUNT(*)
FROM Item
WHERE IsComplated = 0
AND ID Between 1 AND 5000000
How can I run my query on one partition only without scan other partition?
Refer http://msdn.microsoft.com/en-us/library/ms188071.aspx
B. Getting the number of rows in each nonempty partition of a partitioned table or index
The following example returns the number of rows in each partition of table TransactionHistory that contains data. The TransactionHistory table uses partition function TransactionRangePF1 and is partitioned on the TransactionDate column.
To execute this example, you must first run the PartitionAW.sql script against the AdventureWorks2012 sample database. For more information, see PartitioningScript.
USE AdventureWorks2012;
GO
SELECT $PARTITION.TransactionRangePF1(TransactionDate) AS Partition,
COUNT(*) AS [COUNT] FROM Production.TransactionHistory
GROUP BY $PARTITION.TransactionRangePF1(TransactionDate)
ORDER BY Partition ;
GO
C. Returning all rows from one partition of a partitioned table or index
The following example returns all rows that are in partition 5 of the table TransactionHistory.
Note Note
To execute this example, you must first run the PartitionAW.sql script against the AdventureWorks2012 sample database. For more information, see PartitioningScript.
SELECT * FROM Production.TransactionHistory
WHERE $PARTITION.TransactionRangePF1(TransactionDate) = 5 ;