Re: GIN pending list clean up exposure to SQL

On Thu, Jan 28, 2016 at 5:54 AM, Julien Rouhaud
<julien(dot)rouhaud(at)dalibo(dot)com> wrote:
> On 27/01/2016 10:27, Fujii Masao wrote:
>> On Mon, Jan 25, 2016 at 3:54 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
>> wrote:
>>> On Wed, Jan 20, 2016 at 6:17 AM, Fujii Masao
>>> <masao(dot)fujii(at)gmail(dot)com> wrote:
>>>> On Sat, Jan 16, 2016 at 7:42 AM, Julien Rouhaud
>>>> <julien(dot)rouhaud(at)dalibo(dot)com> wrote:
>>>>> On 15/01/2016 22:59, Jeff Janes wrote:
>>>>>> On Sun, Jan 10, 2016 at 4:24 AM, Julien Rouhaud
>>>>>> <julien(dot)rouhaud(at)dalibo(dot)com> wrote:
>>>>>
>>>>> All looks fine to me, I flag it as ready for committer.
>>>>
>>>> When I compiled the PostgreSQL with the patch, I got the
>>>> following error. ISTM that the inclusion of pg_am.h header file
>>>> is missing in ginfast.c.
>>>
>>> Thanks. Fixed.
>>>
>>>> gin_clean_pending_list() must check whether the server is in
>>>> recovery or not. If it's in recovery, the function must exit
>>>> with an error. That is, IMO, something like the following check
>>>> must be added.
>>>>
>>>> if (RecoveryInProgress()) ereport(ERROR,
>>>>
>>>> (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
>>>> errmsg("recovery is in progress"), errhint("GIN pending list
>>>> cannot be cleaned up during recovery.")));
>>>>
>>>> It's better to make gin_clean_pending_list() check whether the
>>>> target index is temporary index of other sessions or not, like
>>>> pgstatginindex() does.
>>>
>>> I've added both of these checks. Sorry I overlooked your early
>>> email in this thread about those.
>>>
>>>>
>>>> + Relation indexRel = index_open(indexoid,
>>>> AccessShareLock);
>>>>
>>>> ISTM that AccessShareLock is not safe when updating the pending
>>>> list and GIN index main structure. Probaby we should use
>>>> RowExclusiveLock?
>>>
>>> Other callers of the ginInsertCleanup function also do so while
>>> holding only the AccessShareLock on the index. It turns out
>>> that there is a bug around this, as discussed in "Potential GIN
>>> vacuum bug"
>>> (http://www.postgresql.org/message-id/flat/CAMkU=1xALfLhUUohFP5v33RzedLVb5aknNUjcEuM9KNBKrB6-Q(at)mail(dot)gmail(dot)com)
>>>
>>>
>>>
> But, that bug has to be solved at a deeper level than this patch.
>>>
>>> I've also cleaned up some other conflicts, and chose a more
>>> suitable OID for the new catalog function.
>>>
>>> The number of new header includes needed to implement this makes
>>> me wonder if I put this code in the correct file, but I don't see
>>> a better location for it.
>>>
>>> New version attached.
>>
>> Thanks for updating the patch! It looks good to me.
>>
>> Based on your patch, I just improved the doc. For example, I added
>> the following note into the doc.
>>
>> + These functions cannot be executed during recovery. + Use
>> of these functions is restricted to superusers and the owner +
>> of the given index.
>>
>> If there is no problem, I'm thinking to commit this version.
>>
>
> Just a detail:
>
> + Note that the cleanup does not happen and the return value is 0
> + if the argument is the GIN index built with <literal>fastupdate</>
> + option disabled because it doesn't have a pending list.
>
> It should be "if the argument is *a* GIN index"
>
> I find this sentence a little confusing, maybe rephrase like this would
> be better:
>
> - Note that the cleanup does not happen and the return value is 0
> - if the argument is the GIN index built with <literal>fastupdate</>
> - option disabled because it doesn't have a pending list.
> + Note that if the argument is a GIN index built with
> <literal>fastupdate</>
> + option disabled, the cleanup does not happen and the return value
> is 0
> + because the index doesn't have a pending list.
>
> Otherwise, I don't see any problem on this version.

Thanks for the review! I adopted the description you suggested.
Just pushed the patch.

Regards,

--
Fujii Masao