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  1. Hive
  2. HIVE-21761

Support table level replication in Hive



    • Type: New Feature
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 4.0.0
    • Component/s: repl
    • Labels:
    • Target Version/s:



      - User needs to define replication policy to replicate any specific table. This enables user to replicate only the business critical tables instead of replicating all tables which may throttle the network bandwidth, storage and also slow-down Hive replication.
      - User needs to define replication policy using regular expressions (such as db.sales_*) and needs to include additional tables which are non-matching given pattern and exclude some tables which are matching given pattern.
      - User needs to dynamically add/remove tables to the list either by manually changing the replication policy during run time.


      1. Hive continue to support DB level replication policy of format <db_name> but logically, we support the policy as <db_name>.'t1|t3| …'.'t*'.
      2. Regular expression can also be supported as replication policy. For example,
        a. <db_name>.'<prefix*>'
        b. <db_name>.'<*suffix>'
        c. <db_name>.'<prefix*suffix>'
        d. <db_name>.'<regex>' 
      3. User can provide include and exclude list to specify the tables to be included in the replication policy.
        a. Include list specifies the tables to be included.
        b. Exclude list specifies the tables to be excluded even if it satisfies the expression in include list.
        c. So the tables included in the policy is a-b.
        d. For backward compatibility, if no include or exclude list is given, then all the tables will be included in  
           the policy.
      4. New format for the Replication policy have 3 parts all separated with Dot (.).
        a. First part is DB name.
        b. Second part is included list. Valid java regex within single quote.
        c. Third part is excluded list. Valid java regex within single quote.
          - <db_name> -- Full DB replication which is currently supported
          - <db_name>.'.*?'  -- Full DB replication
          - <db_name>.'t1|t3'  -- DB replication with static list of tables t1 and t3 included.
          - <db_name>.'(t1*)|t2'.'t100' -- DB replication with all tables having prefix t1 and also include table t2 which doesn’t have prefix t1 and exclude t100 which has the prefix t1.
      5. If the DB property “repl.source.for” is set, then by default all the tables in the DB will be enabled for replication and will continue to archive deleted data to CM path.
      6. REPL DUMP takes 2 inputs along with existing FROM and WITH clause.
        a. REPL DUMP <current_repl_policy> [REPLACE <previous_repl_policy> FROM <last_repl_id> WITH <key_values_list>;
      current_repl_policy and previous_repl_policy can be any format mentioned in Point-4.
        b. REPLACE clause to be supported to take previous repl policy as input. 
        c. Rest of the format remains same.
      7. Now, REPL DUMP on this DB will replicate the tables based on current_repl_policy.
      8. Single table replication of format <db_name>.t1 is not supported. User can provide the same with <db_name>.'t1' format.
      9. If any table is added dynamically either due to change in regular expression or added to include list should be bootstrapped. 
        a. Hive will automatically figure out the list of tables newly included in the list by comparing the current_repl_policy & previous_repl_policy inputs and combine bootstrap dump for added tables as part of incremental dump. As we can combine first incremental with bootstrap dump, it removes the current limitation of target DB being inconsistent after bootstrap unless we run first incremental replication.
        b. If any table is renamed, then it may gets dynamically added/removed for replication based on defined replication policy + include/exclude list. So, Hive will perform bootstrap for the table which is just included after rename. 
        c. Also, if renamed table is excluded from replication policy, then need to drop the old table at target as well.
      10. Only the initial bootstrap load expects the target DB to be empty but the intermediate bootstrap on tables due to regex or inclusion/exclusion list change or renames doesn’t expect the target DB or table to be empty. If any table with same name exist during such bootstrap, the table will be overwritten including data.


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              • Assignee:
                sankarh Sankar Hariappan
                sankarh Sankar Hariappan
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