On 07/23/2013 11:24 AM, Craig Ringer wrote:
> On 07/21/2013 10:42 PM, Миша Тюрин wrote:
>> hi, list, again. the next proposal into auto explain. one would be happy if 
>> could set list of target tables and indexes. sometimes it is very hard to 
>> detect who is using your indexes. but turn total logging on under thousands 
>> transactions per seconds is not seems like nice idea couse size of resulting 
>> log files (cpu utilization might not be so critical)
> That sounds like a good idea - and since auto_explain is a contrib
> module, it could potentially be a way to get into PostgreSQL
> development. The code is in contrib/auto_explain/auto_explain.c .
> The challenge here is that planned queries don't just touch one table or
> index. You'd need to walk the query plan (a graph of Node structures) to
> determine which table(s) and index(es) are touched by the query there's
> something in the sources for it already (I haven't checked).

Showing that I'm still very much learning this area myself, a bit more
looking around found:


which makes it clear that the range table for the query will contain
what you want. I suspect you'll need to find CTEs and subqueries and
extract the relations they touch; I haven't yet checked to see whether
they're aggregated into the top level range table, but suspect not.

You'll find the code in src/backend/nodes/print.c informative and
useful, though not directly reusable.

Reading src/include/nodes/primnodes.h would be a good idea; it shows how
subqueries, etc, are represented.

 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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