Re: Inlining of couple of functions in pl_exec.c improves performance

Hi

so 23. 5. 2020 v 19:03 odesílatel Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>
napsal:

> There are a couple of function call overheads I observed in pl/pgsql
> code : exec_stmt() and exec_cast_value(). Removing these overheads
> resulted in some performance gains.
>
> exec_stmt() :
>
> plpgsql_exec_function() and other toplevel block executors currently
> call exec_stmt(). But actually they don't need to do everything that
> exec_stmt() does. So they can call a new function instead of
> exec_stmt(), and all the exec_stmt() code can be moved to
> exec_stmts(). The things that exec_stmt() do, but are not necessary
> for a top level block stmt, are :
>
> 1. save_estmt = estate->err_stmt; estate->err_stmt = stmt;
> For top level blocks, saving the estate->err_stmt is not necessary,
> because there is no statement after this block statement. Anyways,
> plpgsql_exec_function() assigns estate.err_stmt just before calling
> exec_stmt so there is really no point in exec_stmt() setting it again.
>
> 2. CHECK_FOR_INTERRUPTS()
> This is not necessary for toplevel block callers.
>
> 3. exec_stmt_block() can be directly called rather than exec_stmt()
> because func->action is a block statement. So the switch statement is
> not necessary.
>
> But this one might be necessary for toplevel block statement:
> if (*plpgsql_plugin_ptr && (*plpgsql_plugin_ptr)->stmt_beg)
> ((*plpgsql_plugin_ptr)->stmt_beg) (estate, stmt);
>
> There was already a repetitive code in plpgsql_exec_function() and
> other functions around the exec_stmt() call. So in a separate patch
> 0001*.patch, I moved that code into a common function
> exec_toplevel_block(). In the main patch
> 0002-Get-rid-of-exec_stmt-function-call.patch, I additionally called
> plpgsql_plugin_ptr->stmt_beg() inside exec_toplevel_block(). And moved
> exec_stmt() code into exec_stmts().
>
>
>
> exec_cast_value() :
>
> This function does not do the casting if not required. So moved the
> code that actually does the cast into a separate function, so as to
> reduce the exec_cast_value() code and make it inline. Attached is the
> 0003-Inline-exec_cast_value.patch
>
>
> Testing
> ----------
>
> I used two available VMs (one x86_64 and the other arm64), and the
> benefit showed up on both of these machines. Attached patches 0001,
> 0002, 0003 are to be applied in that order. 0001 is just a preparatory
> patch.
>
> First I tried with a simple for loop with a single assignment
> (attached forcounter.sql)
>
> By inlining of the two functions, found noticeable reduction in
> execution time as shown (figures are in milliseconds, averaged over
> multiple runs; taken from 'explain analyze' execution times) :
> ARM VM :
> HEAD : 100 ; Patched : 88 => 13.6% improvement
> x86 VM :
> HEAD : 71 ; Patched : 66 => 7.63% improvement.
>
> Then I included many assignment statements as shown in attachment
> assignmany.sql. This showed further benefit :
> ARM VM :
> HEAD : 1820 ; Patched : 1549 => 17.5% improvement
> x86 VM :
> HEAD : 1020 ; Patched : 869 => 17.4% improvement
>
> Inlining just exec_stmt() showed the improvement mainly on the arm64
> VM (7.4%). For x86, it was 2.7%
> But inlining exec_stmt() and exec_cast_value() together showed
> benefits on both machines, as can be seen above.
>

FOR counter IN 1..1800000 LOOP
id = 0; id = 0; id1 = 0;
id2 = 0; id3 = 0; id1 = 0; id2 = 0;
id3 = 0; id = 0; id = 0; id1 = 0;
id2 = 0; id3 = 0; id1 = 0; id2 = 0;
id3 = 0;
END LOOP;

This is not too much typical PLpgSQL code. All expressions are not
parametrized - so this test is little bit obscure.

Last strange performance plpgsql benchmark did calculation of pi value. It
does something real

Regards

Pavel

> --
> Thanks,
> -Amit Khandekar
> Huawei Technologies
>