Re: RFD: Discarded tuple count for SeqScan nodes in EXPLAIN ANALYZE

Hi,

On 05/22/2009 03:42 PM, Heikki Linnakangas wrote:
> Andres Freund wrote:
>> When analyzing the plan of a query I often find myself questioning
>> whether an additional index may be sensible, or if it is sensible that
>> a SeqScan is used if an index is available.
>>
>> The current EXPLAIN ANALYZE only shows the number of tuples matching
>> the qualifier of an SeqScan Node - for analyzing the above situation
>> it is at least equally interesting how many tuples were read and
>> discarded.
>> Good idea - Bad idea?
> Isn't the discarded count always equal to (# of rows in table - matched
> tuples)? Seems pretty redundant to me.
Not for EXISTS(), LIMIT and similar.

Also when looking at more complex plans its quite a nuisance to go
through all participating tables and do a separate count(*). Especially
its not your plan but some clients plan etc.

Andres