Modifying Postgresql Optimizer to select optimal memory
Hello everyone,
We are currently working on a DBMS course project that requires us to
modify postgresql optimizer. We need to vary work_mem within a range and
note down the cost at those points(allocated memory) after 'explain'
operation and then select the optimal tradeoff. We were changing
"postgresql-9.1.12/src/backend/optimizer/plan/planner.c" where we created a
new function mem_tradeoff() that calls planner() within a for loop for the
varying memory. This mem_tradeoff() is called from pg_plan_query() in
"postgresql-9.1.12/src/backend/tcop/postgres.c". The problem is, if the for
loop runs only one iteration, everything is fine, but if we print
plan->planTree->total_cost, it is printed 132 times for any query. Also if
the for loop runs more than one iteration, we get a segmentation fault. Any
help is very much appreciated.
Thank you,
Sayan
--
Don't kill the dream - execute it.
Sayan Biswas <formal.sayan@gmail.com> writes:
Hello everyone,
We are currently working on a DBMS course project that requires us to
modify postgresql optimizer. We need to vary work_mem within a range and
note down the cost at those points(allocated memory) after 'explain'
operation and then select the optimal tradeoff. We were changing
"postgresql-9.1.12/src/backend/optimizer/plan/planner.c" where we created a
new function mem_tradeoff() that calls planner() within a for loop for the
varying memory. This mem_tradeoff() is called from pg_plan_query() in
"postgresql-9.1.12/src/backend/tcop/postgres.c". The problem is, if the for
loop runs only one iteration, everything is fine, but if we print
plan->planTree->total_cost, it is printed 132 times for any query. Also if
the for loop runs more than one iteration, we get a segmentation fault. Any
help is very much appreciated.
The comment on standard_planner might help you:
* Note to plugin authors: standard_planner() scribbles on its Query input,
* so you'd better copy that data structure if you want to plan more than once.
regards, tom lane
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