Re: [HACKERS] Restrict concurrent update/delete with UPDATE of partition key

On Tue, Nov 28, 2017 at 5:58 PM, amul sul <sulamul(at)gmail(dot)com> wrote:
> On Sat, Nov 25, 2017 at 11:39 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> On Thu, Nov 23, 2017 at 5:18 PM, amul sul <sulamul(at)gmail(dot)com> wrote:
>>> On Sat, Nov 11, 2017 at 1:05 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>>> On Wed, Sep 27, 2017 at 7:07 AM, amul sul <sulamul(at)gmail(dot)com> wrote:
>>>>>
> [...]
>> Few comments:
>>
> Thanks for looking at the patch, please find my comments inline:
>
>> 1.
>> @@ -1480,6 +1493,10 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,
>> ereport(ERROR,
>> (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
>> errmsg("could not serialize access due to concurrent update")));
>> + if (!BlockNumberIsValid(BlockIdGetBlockNumber(&((hufd.ctid).ip_blkid))))
>> + ereport(ERROR,
>> + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
>> + errmsg("tuple to be updated was already moved to an another
>> partition due to concurrent update")));
>>
>> Why do you think we need this check in the OnConflictUpdate path? I
>> think we don't it here because we are going to relinquish this version
>> of the tuple and will start again and might fetch some other row
>> version. Also, we don't support Insert .. On Conflict Update with
>> partitioned tables, see[1], which is also an indication that at the
>> very least we don't need it now.
>>
> Agreed, even though this case will never going to be anytime soon
> shouldn't we have a check for invalid block id? IMHO, we should have
> this check and error report or assert, thoughts?
>

I feel adding code which can't be hit (even if it is error handling)
is not a good idea. I think having an Assert should be okay, but
please write comments to explain the reason for adding an Assert.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com