MySQL Bugs: #21472: question about the query against to the federated engine tables

Bug #21472	question about the query against to the federated engine tables
Submitted:	7 Aug 2006 7:13	Modified:	26 Aug 2006 12:46
Reporter:	ming lu	Email Updates:
Status:	Duplicate	Impact on me:	None
Category:	MySQL Server: Federated storage engine	Severity:	S5 (Performance)
Version:	5.1.12	OS:	Linux (linux)
Assigned to:		CPU Architecture:	Any

Description:
I have a question about the query against to the federated engine tables. As the following example:

	"select Id,name from e01_system.category" 
	Note: the "e01_system.category" is a federated table.

I select only tow fields from the federated table "category" with the above sql statement. But it seemed as if gets all the fields of the table (the table has more then ten fields actually), so the performance of the sql stetement is very slow when the table's size is very big.I conclude this through monitoring the throughput of the network with a network tool named "sniffer". I think the federated table works not as what i expected.

   The problem will reduce performance of the database.

How to repeat:
1. create a innodb table with more than ten fields
  example: 
  create table category (id int, name varchar(20), number int, note varchar(100))

2. insert some data into the table
3. create a federated table 
  example: federated_category
4. excute a query sql like this:
   select id, name from federated_category;
   at the same time, monitor the throughput of the network with a network tool

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I think the problem is an important factor to reducing query performance against to federated engine tables. How about describe the problem's Severity as S5(performance)?

Looks like a duplicate of bug #19054. At least, the reason is the same (and fix should be similar - not to select all columns from remote table).