Re: Why overhead of SPI is so large?

Some more information...
First of all I found out that marking PL/pgSQL function as immutable significantly increase speed of its execution:
19808 ms vs. 27594. It happens because exec_eval_simple_expr is taken snapshot if function is volatile (default).
I wonder if PL/pgSQL compiler can detect that evaluated expression itself is actually immutable  and there is no need to take snapshot
for each invocation of this function. Also I have tried yet another PL language - JavaScript, which is now new outsider, despite to the fact that
v8 JIT compiler is very good.

Implementation	time (ms)
PL/v8	41550
PL/Lua	32220
PL/pgSQL	19808
C/SPI	9406
SQL	7399
SQL (JIT)	5532
С/coreAPI	2873

-- 
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company