Hot Swapping of Tables in Hive

Here are the steps to hot swap a table in Hive when you manually load data in them. Hot Swapping the table allows you to refresh an entire table without any downtime thus making your table always available for querying. With this approach you Lock the table but it is only for a fraction of a second. This is useful when you want to change the definition of a table or reload the whole table without downtime. Hive 11 allows you to maintain lock on a table which you can later drop and re-create.

Here are the steps for the swap:

  1. Store the data in a staging location in HDFS
  2. Get EXCLUSIVE LOCK on the Hive table (using LOCK TABLE tablename) - so queries have to wait to until we finish the refresh
  3. Delete the underlying Hive folder (e.g. /user/hive/warehouse/user.db/tablename). We have to delete first because of https://issues.apache.org/jira/browse/HDFS-4142 and https://issues.apache.org/jira/browse/HADOOP-9382)
  4. Move the staging folder to the hive directory. (e.g. mv /user/staging/tablename /user/hive/warehouse/user/db/tablename)
  5. Release LOCK on the table
 
36
Kudos
 
36
Kudos

Now read this

Create a file of size x bytes

One of the common requirements I run across in moving data around is finding if I’m doing it the fastest way possible. A good indicator of speed is to find out how long it takes for a large file to get copied from one server to another.... Continue →