Fwd: Query Optimizer Postgresql

Hello Everyone,
I had some questions about the query optimization engine and will be
grateful if someone can answer them

---------- Forwarded message ---------
From: Sumit Chaturvedi <sumit(dot)chaturvedi(at)gmail(dot)com>
Date: Sun, Oct 14, 2018 at 8:50 PM
Subject: Query Optimizer Postgresql
To: <bruce(at)momjian(dot)us>
Cc: Adwait Godbole <godbole15(at)gmail(dot)com>, Nilay Pande <nilay017(at)gmail(dot)com>,
<nitishj(at)cse(dot)iitb(dot)ac(dot)in>

Hello Sir

My friends and I are trying to come up with an experimental implementation
of Join Optimization within PostgreSQL. We have a few questions about the
code and will be grateful if you could address them.

We found that the dynamic programming algorithm is implemented in
standard_join_search(). We realized that the optimal path is stored in the
cheapest_path field in the RelOptInfo struct that is returned.

Since in our implementation, we are only trying to optimize on the join
order, we were wondering what all changes would we need to make without
breaking the code? In other words, what additional state would we need to
modify if we were to rewrite the standard_join_search() method such that
everything works out well.

Also, since our implementation would need the stats generated by ANALYZE
command, what interface is available for that. For example I noticed the
function call set_cheapest(rel). Can I simply use this call once I have
populated my RelOptInfo->pathlist and accept it to consult the statistics
and appropriately populate RelOptInfo->cheapest_path.

Finally, what additional care should we take to handle queries containing
asymmetric joins or joins in subqueries?

By the way, I have watched your talks on Postgres Internals and the Query
Optimization Engine and as a student of databases, I find them
enlightening.

Thank You

--
Sumit Chaturvedi

--
Sumit Chaturvedi