Postgres-XC tutorial PDF - PGCon
Postgres-XC tutorial PDF - PGCon
Postgres-XC tutorial PDF - PGCon
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Replicated tables multirow operations<br />
●<br />
Example: aggregation on replicated table<br />
EXPLAIN VERBOSE SELECT sum(val) FROM tab1 GROUP BY val2;<br />
QUERY PLAN<br />
<br />
HashAggregate Groups rows on coordinator, N(groups) < N(rows)<br />
Output: sum(val), val2<br />
> Data Node Scan on tab1<br />
Brings all the rows from one datanode to coordinator.<br />
Output: val, val2<br />
Node/s: datanode_1<br />
Remote query: SELECT val, val2 FROM ONLY tab1 WHERE true<br />
May 16th, 2012 <strong>Postgres</strong><strong>XC</strong> 48
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