Re: [Postgres-xc-developers] Replicated update and delete

[Ashutosh B. <ash...@en...>]

WCO on datanodes should be working fine, so that shouldn't be a problem.


On Thu, Feb 13, 2014 at 12:13 PM, 鈴木 幸市 <ko...@in...> wrote:

>  Are you sure that this does not come up with any bad side effects to
> support WCO in 1.3?
> ---
> Koichi Suzuki
>
>  2014/02/13 15:24、Ashutosh Bapat <ash...@en...> のメール：
>
>  One more solution would be to use cursors for replicated tables. The
> idea is to open cursors on all the copies of the table and append the query
> with an ORDER BY clause on all the columns. Thus we are sure that the
> current of each of these cursors point to same row on all the copies. While
> fetching a row from a replicated table, we fetch from all the cursors and
> choose only one row for the data processing. While updating or deleting we
> send UPDATE or DELETE with WHERE CURRENT OF. The down side of this approach
> is that, if there are coordinator quals, we will end up locking more rows
> than necessary, increasing the probability of the deadlock but at least
> there won't be a necessary restriction of having primary or unique key and
> we won't break backward compatibility.
>
>  If there two identical rows, we might mix the update from different
> nodes, but then who knew which of them were corresponded across the nodes
> to start with.
>
>
> On Thu, Feb 13, 2014 at 9:45 AM, Koichi Suzuki <koi...@gm...>wrote:
>
>> Hi,
>>
>> I tested the patch and found that primary key is mandatory.   We need
>> to modify regression test considerably to give each replicated table
>> primary keys.
>>
>> I think this patch helps but I'm not afraid this is good, especially
>> when we try to take XC features back to PG.
>>
>> Did you post another patch to use all column values if primary key is
>> not available?
>>
>> I think better way is as follows:
>>
>> 1) If primary key is defined, use it,
>> 2) If not, create a primary key as system column, the size should be
>> 64bit.
>> 3) If primary key is added to a replicated table, remove system primary
>> key.
>>
>> The value of primary key can be obtained as follows:
>>
>> 1) add new column to pgxc_class catalog to represent maximum value of
>> the system primary key,
>> 2) when first "insert" is done to the primary node, system primary key
>> value is taken from 1) and 1) is updated.  The value is returned to
>> the coordinator to be propagated to other nodes.
>> 3) when subsequent "insert" is being done, system primary key value is
>> added to the column value.   In this case, each datanode updates 1)
>> column value if it is larger than the current maximum value.
>>
>> 3) is important to change primary node to another.   This is needed to
>> carry over the primary node to another.
>>
>> ALTER TABLE should take care of them.
>>
>> Other issues are:
>>
>> 4) pg_dump/pg_dumpall should not include this system column value,
>> 5) cluster may need to handle this too to repack system primary key
>> value (not now but at least in 1.3 or later).
>>
>> Regards;
>> ---
>> Koichi Suzuki
>>
>>
>> 2013-11-02 9:26 GMT+09:00 Mason Sharp <ms...@tr...>:
>>  > Please see attached patch that tries to address the issue of XC using
>> CTID
>> > for replicated updates and deletes when it is evaluated at a coordinator
>> > instead of being pushed down.
>> >
>> > The problem here is that CTID could be referring to a different tuple
>> > altogether on a different data node, which is what happened for one of
>> our
>> > Postgres-XC support customers, leading to data issues.
>> >
>> > Instead, the patch looks for a primary key or unique index (with the
>> primary
>> > key preferred) and uses those values instead of CTID.
>> >
>> > The patch could be improved further.  Extra parameters are set even if
>> not
>> > used in the execution of the prepared statement sent down to the data
>> nodes.
>> >
>> > Regards,
>> >
>> >
>> > --
>> > Mason Sharp
>> >
>> > TransLattice - http://www.translattice.com
>> > Distributed and Clustered Database Solutions
>> >
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>
>
> --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>
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-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company