Re: [PATCH] Add features to pg_stat_statements

On 2020/11/09 18:02, Seino Yuki wrote:
> 2020-11-09 15:39 に Seino Yuki さんは書きました:
>>>>
>>>> However, let me confirm the following.
>>>>> Is this information really useful?
>>>>> If there is no valid use case for this, I'd like to drop it.
>>>>> Thought?
>>>>
>>>> I thought it would be easy for users to see at a glance that if there is a case I assumed,
>>>> if the last modified date and time is old, there is no need to adjust at all, and if the
>>>> last modified date and time is recent, it would be easy for users to understand that the
>>>> parameters need to be adjusted.
>>>> What do you think?
>>>
>>> Even without the last deallocation timestamp, you can presume
>>> when the deallocation of entries happened by periodically monitoring
>>> the total number of deallocations and seeing those history. Or IMO
>>> it's better to log whenever the deallocation happens as proposed upthread.
>>> Then you can easily check the history of occurrences of deallocations
>>> from the log file.
>>>
>>> Regards,
>>
>> +1.I think you should output the deallocation history to the log as well.
>>
>> In light of the above, I've posted a patch that reflects the points made.
>>
>> Regards,
>
> Sorry. There was a typo in the documentation correction.
> I'll post a patch to fix it.

Thanks for updating the patch!

+ pgss_info->dealloc = 0;
+ SpinLockInit(&pgss_info->mutex);
+ Assert(pgss_info->dealloc == 0);

Why is this assertion check necessary? It seems not necessary.

+ {
+ Assert(found == found_info);

Having pgssSharedState and pgssInfoCounters separately might make
the code a bit more complicated like the above? If this is true, what about
including pgssInfoCounters in pgssSharedState?

PGSS_FILE_HEADER needs to be changed since the patch changes
the format of pgss file?

+ /* Read pgss_info */
+ if (feof(file) == 0)
+ if (fread(pgss_info, sizeof(pgssInfoCounters), 1, file) != 1)
+ goto read_error;

Why does feof(file) need to be called here?

+pgss_info_update(void)
+{
+ {

Why is the second "{" necessary? It seems redundant.

+pgss_info_reset(void)
+{
+ {

Same as above.

+pg_stat_statements_info(PG_FUNCTION_ARGS)
+{
+ int64 d_count = 0;
+ {

Same as above.

+ SpinLockAcquire(&c->mutex);
+ d_count = Int64GetDatum(c->dealloc);
+ SpinLockRelease(&c->mutex);

Why does Int64GetDatum() need to be called here? It seems not necessary.

+ <varlistentry>
+ <term>
+ <function>pg_stat_statements_info() returns bigint</function>
+ <indexterm>
+ <primary>pg_stat_statements_info</primary>
+ </indexterm>
+ </term>

Isn't it better not to expose pg_stat_statements_info() function in the
document because pg_stat_statements_info view is enough and there
seems no use case for the function?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION