Re: Table AM Interface Enhancements

Hi, Nikita!

On Wed, 29 Nov 2023 at 18:27, Nikita Malakhov <hukutoc(at)gmail(dot)com> wrote:

> Hi,
>
> Pavel, as far as I understand Alexander's idea assertion and especially
> ereport
> here does not make any sense - this method is not considered to report
> error, it
> silently calls if there is underlying [free] function and simply falls
> through otherwise,
> also, take into account that it could be located in the uninterruptible
> part of the code.
>
> On the whole topic I have to
>
> On Wed, Nov 29, 2023 at 4:56 PM Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>
> wrote:
>
>> Hi, Alexander!
>>
>>> I'm planning to review some of the other patches from the current
>>> patchset soon.
>>>
>>
>> I've looked into the patch 0003.
>> The patch looks in good shape and is uncontroversial to me. Making memory
>> structures to be dynamically allocated is simple enough and it allows to
>> store complex data like lists etc. I consider places like this that expect
>> memory structures to be flat and allocated at once are because the was no
>> need in more complex ones previously. If there is a need for them, I think
>> they could be added without much doubt, provided the simplicity of the
>> change.
>>
>> For the code:
>> +static inline void
>> +table_free_rd_amcache(Relation rel)
>> +{
>> + if (rel->rd_tableam && rel->rd_tableam->free_rd_amcache)
>> + {
>> + rel->rd_tableam->free_rd_amcache(rel);
>> + }
>> + else
>> + {
>> + if (rel->rd_amcache)
>> + pfree(rel->rd_amcache);
>> + rel->rd_amcache = NULL;
>> + }
>>
>> here I suggest adding Assert(rel->rd_amcache == NULL) (or maybe better an
>> error report) after calling free_rd_amcache to be sure the custom
>> implementation has done what it should do.
>>
>> Also, I think some brief documentation about writing this custom method
>> is quite relevant maybe based on already existing comments in the code.
>>
>> Kind regards,
>> Pavel
>>
>
> When we do default single chunk routine we invalidate rd_amcache pointer,
+ if (rel->rd_amcache)
+ pfree(rel->rd_amcache);
+ rel->rd_amcache = NULL;

If we delegate this to method, my idea is to check the method
implementation don't leave this pointer valid.
If it's not needed, I'm ok with it, but to me it seems that the check I
proposed makes sense.

Regards,
Pavel