Re: Auto-explain patch

Dean Rasheed <dean_rasheed(at)hotmail(dot)com> wrote:

> > An arguable part is initializing instruments in ExecutorRun_hook.
> > The initialization should be done in ExecutorStart normally, but
> > it is too late in the hook. Is it safe? or are there any better idea?
>
> How about adding a new hook to control instrumentation of queries in
> ExecutorStart? Something like:
>
> typedef bool (*ExecutorDoInstrument_hook_type) (QueryDesc *queryDesc, int eflags);
> extern PGDLLIMPORT ExecutorDoInstrument_hook_type ExecutorDoInstrument_hook;

I think it is not good to have any single-purpose hooks -- a new global
variable "bool force_instrument" would be enough for the purpose ;-)

I'd like to suggest on-demand allocation of instruments instead.
PlanState->instrument is not only a runtime statstics collector, but also
represents whether instrumentation is enabled or not. However, we also
have the same information in EState->es_insrument. If we use it instread
of NULL check, we could initialize instrument fields in executor.

[src/backend/executor/execProcnode.c]
ExecProcNode(PlanState *node)
{
...
if (node->state->es_instrument)
{
if (node->instrument == NULL)
node->instrument = InstrAlloc(1, long_lived_memory_context);
InstrStartNode(node->instrument);
}

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center