Type: New Feature
Affects Version/s: None
Release Note:From the shell's doc:
# set table / table-cf to be replicable for a peer, for a table without
# an explicit column-family list, all replicable column-families (with
# replication_scope == 1) will be replicated
hbase> set_peer_tableCFs '2', "table1; table2:cf1,cf2; table3:cfA,cfB"
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.