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From "Feng Honghua (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8751) Enable peer cluster to choose/change the ColumnFamilies/Tables it really want to replicate from a source cluster
Date Mon, 17 Jun 2013 02:01:21 GMT
Feng Honghua created HBASE-8751:
-----------------------------------

             Summary: Enable peer cluster to choose/change the ColumnFamilies/Tables it really
want to replicate from a source cluster
                 Key: HBASE-8751
                 URL: https://issues.apache.org/jira/browse/HBASE-8751
             Project: HBase
          Issue Type: Improvement
          Components: Replication
            Reporter: Feng Honghua


Consider scenarios (all cf are with replication-scope=1):

1) cluster S has 3 tables, table A has cfA,cfB, table B has cfX,cfY, table C has cf1,cf2.

2) cluster X wants to replicate table A : cfA, table B : cfX and table C from cluster S.

3) cluster Y wants to replicate table B : cfY, table C : cf2 from cluster S.

Current replication implementation can't achieve this since it'll push the data of all the
replicatable column-families from cluster S to all its peers, X/Y in this scenario.

This improvement provides a fine-grained replication theme which enable peer cluster to choose
the column-families/tables they really want from the source cluster:

A). Set the table:cf-list for a peer when addPeer:
  hbase-shell> add_peer '3', "zk:1100:/hbase", "table1; table2:cf1,cf2; table3:cf2"

B). View the table:cf-list config for a peer using show_peer_tableCFs:
  hbase-shell> show_peer_tableCFs "1"

C). Change/set the table:cf-list for a peer using set_peer_tableCFs:
  hbase-shell> set_peer_tableCFs '2', "table1:cfX; table2:cf1; table3:cf1,cf2"

In this theme, replication-scope=1 only means a column-family CAN be replicated to other clusters,
but only the 'table:cf-list list' determines WHICH cf/table will actually be replicated to
a specific peer.

To provide back-compatibility, empty 'table:cf-list list' will replicate all replicatable
cf/table. (this means we don't allow a peer which replicates nothing from a source cluster,
we think it's reasonable: if replicating nothing why bother adding a peer?)

This improvement addresses the exact problem raised  by the first FAQ in "http://hbase.apache.org/replication.html":
  "GLOBAL means replicate? Any provision to replicate only to cluster X and not to cluster
Y? or is that for later?
  Yes, this is for much later."

I also noticed somebody mentioned "replication-scope" as integer rather than a boolean is
for such fine-grained replication purpose, but I think extending "replication-scope" can't
achieve the same replication granularity flexibility as providing above per-peer replication
configurations.

This improvement has been running smoothly in our production clusters (Xiaomi) for several
months.

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