Postgres-XC tutorial PDF - PGCon
Postgres-XC tutorial PDF - PGCon
Postgres-XC tutorial PDF - PGCon
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●<br />
JOINs<br />
Example: Join on distribution key<br />
EXPLAIN VERBOSE SELECT * FROM tab1, tab2 WHERE tab1.val = tab2.val;<br />
QUERY PLAN<br />
<br />
Nested Loop – Perform JOIN on coordinator.<br />
Output: tab1.val, tab1.val2, tab2.val, tab2.val2<br />
Join Filter: (tab1.val = tab2.val)<br />
Queries to datanodes to fetch the rows from tab1 and tab2<br />
> Data Node Scan on tab1<br />
Output: tab1.val, tab1.val2<br />
Remote query: SELECT val, val2 FROM ONLY tab1 WHERE true<br />
> Data Node Scan on tab2<br />
Output: tab2.val, tab2.val2<br />
Remote query: SELECT val, val2 FROM ONLY tab2 WHERE true<br />
May 16th, 2012 <strong>Postgres</strong><strong>XC</strong> 55