Sunday, July 19, 2015

2015-07-19 Sunday - MySQL Federated Engine

I'm doing some research this weekend on MySQL's Federated Engine.  This posting is placeholder for collecting various information I find that might be of interest to others.

  • FEDERATED table does not support indexes in the usual sense; because access to the table data is handled remotely, it is actually the remote table that makes use of indexes. This means that, for a query that cannot use any indexes and so requires a full table scan, the server fetches all rows from the remote table and filters them locally. This occurs regardless of any WHERE or LIMIT used with this SELECT statement; these clauses are applied locally to the returned rows
  • Queries that fail to use indexes can thus cause poor performance and network overload. In addition, since returned rows must be stored in memory, such a query can also lead to the local server swapping, or even hanging.

  • "a number of limitations and due to network latency are rarely used...not enabled by default and is no longer maintained by Oracle and it's use is discouraged"

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