When alter the partition column name of the partition table(named partitioned_table), the corresponding directory in the HDFS does not change. However, the deletion and movement of partitions can be changed in the HDFS.And the the column name is changed using "show partitioin partitioned_table".
Hive version is 4.0.0-alpha-2.
Use the below statement to alter partiton column name.
ALTER TABLE table_name PARTITION
(partition_column = partition_col_value,
partition_column = partition_col_value)
RENAME TO PARTITION (partition_column = partition_col_value,
partition_column = partition_col_value);
Why and how to change the corresponding directory in HDFS when alter partition column name in Hive.
When you alter a partition, it only affects the Hive Metastore, and will never affect data in HDFS. For that, you need to explicitly insert data into the Hive table at that partition, or issue an hdfs mv command, then MSCK REPAIR Hive query to fix the metadata
Related
I have text file with snappy compression partitioned by field 'process_time' (result of Flume job). Example: hdfs://data/mytable/process_time=25-04-2019
This is my script for create table:
CREATE EXTERNAL TABLE mytable
(
...
)
PARTITIONED BY (process_time STRING)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE
LOCATION '/data/mytable/'
TBLPROPERTIES("textfile.compress"="snappy");
The result of queries against this table are allways 0 (but I know that there are some data). Any help?
Thanks!
As you are creating external table on top of HDFS directory then to add the partitions to the hive table we need to run either of these commands.
if any partition added to HDFS directly(instead of using insert queries) then hive doesn't know about the newly added partitions, so we need to run either msck (or) add partitions to add newly added partitions to hive table.
To add all partitions to hive table:
hive> msck repair table <db_name>.<table_name>;
(or)
To manually add each partition to hive table:
hive> alter table <db_name>.<table_name> add partition(process_time="25-04-2019")
location '/data/mytable/process_time=25-04-2019';
For more details refer to this link.
My hive table is partitioned with column 'job_id'. When I dump the data in the hdfs location of the table, then it is creating a partition with name 'JOB_ID' and my hive table is not recognizing it.
I have tried msck repair table command but that didn't helped either.
For external Hive tables you need to add new partition manually as follows:
ALTER TABLE table_name ADD PARTITION (job_id='927') location 'hdfs://some_location/job_id=927'
I found out that the partition name should always be in lowercase letter.
Here is the link:
https://medium.com/a-muggles-pensieve/hive-partition-column-name-camelcase-bad-idea-bc203d6e65da
I have an external table, now I want to add partitions to it. I have 224 unique city id's and I want to just write alter table my_table add partition (cityid) location /path; but hive complains, saying that I don't provide anything for the city id value, it should be e.g. alter table my_table add partition (cityid=VALUE) location /path;, but I don't want to run alter table commands for every value of city id, how can I do it for all id's in one go?
This is what hive command line looks like:
hive> alter table pavel.browserdata add partition (cityid) location '/user/maria_dev/data/cityidPartition';
FAILED: ValidationFailureSemanticException table is not partitioned but partition spec exists: {cityid=null}
Partition on physical level is a location (separate location for each value, usually looks like key=value) with data files. If you already have partitions directory structure with files, all you need is to create partitions in Hive metastore, then you can point your table to the root directory using ALTER TABLE SET LOCATION, then use MSCK REPAIR TABLE command. The equivalent command on Amazon Elastic MapReduce (EMR)'s version of Hive is: ALTER TABLE table_name RECOVER PARTITIONS. This will add Hive partitions metadata. See manual here: RECOVER PARTITIONS
If you have only not-partitioned table with data in it's location, then adding partitions will not work because the data needs to be reloaded, you need to:
Create another partitioned table and use insert overwrite to load partition data using dynamic partition load:
set hive.exec.dynamic.partition=true;
set hive.exec.dynamic.partition.mode=nonstrict;
insert overwrite table2 partition(cityid)
select col1, ... colN,
cityid
from table1; --partitions columns should be last in the select
This is quite efficient way to reorganize your data.
After this you can delete source table and rename your target table.
I have an existing S3 folder structure like this,
s3://mydata/{country}/{date}/
{country} could be any of 30 different countries
{date} could be any date since 20150101
How can I read this in Hive by treating {country} as partition and {date} as sub partition ?
You can use the Hive DDL statement ALTER TABLE ADD PARTITION
ALTER TABLE mydata
ADD PARTITION (country='south-africa', date='20191024')
LOCATION 's3://mydata/south-africa/20191024/';
You can script this using a shell script, and passing each statement to Hive like hive -e 'ALTER TABLE $TABLE ADD PARTITION $PARTITION_SPEC LOCATION $PARTITION_LOCATION'
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-AddPartitions
I have created an external table in Hive with at this location :
CREATE EXTERNAL TABLE tb
(
...
)
PARTITIONED BY (datehour INT)
ROW FORMAT SERDE 'com.cloudera.hive.serde.JSONSerDe'
LOCATION '/user/cloudera/data';
The data is present in the folder but when I query the table, it returns nothing. The table is structured in a way that it fits the data structure.
SELECT * FROM tb LIMIT 3;
Is there a kind of permission issue with Hive tables: do specific users have permissions to query some tables?
Do you know some solutions or workarounds?
You have created your table as partitioned table base on column datehour, but you are putting your data in /user/cloudera/data. Hive will look for data in /user/cloudera/data/datehour=(some int value). Since it is an external table hive will not update the metastore. You need to run some alter statement to update that
So here are the steps for external tables with partition:
1.) In you external location /user/cloudera/data, create a directory datehour=0909201401
OR
Load data using: LOAD DATA [LOCAL] INPATH '/path/to/data/file' INTO TABLE partition(datehour=0909201401)
2.) After creating your table run a alter statement:
ALTER TABLE ADD PARTITION (datehour=0909201401)
Hope it helps...!!!
When we create an EXTERNAL TABLE with PARTITION, we have to ALTER the EXTERNAL TABLE with the data location for that given partition. However, it need not be the same path as we specify while creating the EXTERNAL TABLE.
hive> ALTER TABLE tb ADD PARTITION (datehour=0909201401)
hive> LOCATION '/user/cloudera/data/somedatafor_datehour'
hive> ;
When we specify LOCATION '/user/cloudera/data' (though its optional) while creating an EXTERNAL TABLE we can take some advantage of doing repair operations on that table. So when we want to copy the files through some process like ETL into that directory, we can sync up the partition with the EXTERNAL TABLE instead of writing ALTER TABLE statement to create another new partition.
If we already know the directory structure of the partition that HIVE would create, we can simply place the data file in that location like '/user/cloudera/data/datehour=0909201401/data.txt' and run the statement as shown below:
hive> MSCK REPAIR TABLE tb;
The above statement will sync up the partition to the hive meta store of the table "tb".