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

[Abbas B. <abb...@en...>]

Here are the results of DBT-1 runs on the buildfarm.
The patch solves the duplicate key error problem that was reported and the
added test cases behave as expected.

ID 115 : Without the patch.
ID 114 : With the patch.

For reference see the datanode log for id 115, it shows the duplicate key
errors where as the same log in ID 114 does not show any such errors.

The links showing the logs are as follows
https://61.197.200.11/files/115/dbt1/pg_log/node01/datanode_dn1/postgresql-2014-02-25_112551.log
https://61.197.200.11/files/114/dbt1/pg_log/node01/datanode_dn1/postgresql-2014-02-25_102910.log



I have however observed a problem that has nothing to do with the current
patch.

Consider the TPS graphs of ID 112 and 102
The links are as follows:
https://61.197.200.11/tps_chart/index/112
https://61.197.200.11/tps_chart/index/102

ID 112 is using commit ID 9b6be5b8ba66eb9e083a4a80669e7d41a2cea3dc, which
is a recent commit to branch REL1_2_STABLE, whereas ID 102 is using commit
ID ea3dbab2dbebe770c0e90132281dbb37ae31fdcc which is an older commit to
branch master_pg93_merge.

Notice that the TPS for ID 102 stays stable at 13000 whereas the TPS for ID
112 deteriorates over time and the max achieved TPS is also reduced  to
7000 only.

Knowing that the branch REL1_2_STABLE was created using master_pg93_merge
this needs to be investigated further to find which commit/step is causing
this deterioration.

Best Regards



On Tue, Feb 25, 2014 at 9:33 AM, Abbas Butt <abb...@en...>wrote:

> Hi,
> Attached please find revised and updated patch that performs
> updates/deletes to replicated tables based on either primary key or unique
> index under the following conditions
> 1. The replicated table has either a primary key or a unique index defined.
> 2. The query is not changing the primary key itself.
> Otherwise ctid is used, like we were using previously.
>
> Getting a clean regression with the patch was not easy. Lot of issues had
> to be fixed especially with deletes.
> Regression and DBT-1 now work cleanly after that patch.
> Test cases are added in the regression to make sure the
> added functionality is working fine.
>
> The attached patch does not include the cursors approach as of now.
> The patch to use cursors in case when primary key cannot be used is not
> complete yet. The changes in the planner are done, but the changes in
> executor are still to do. The current executor does not work with a fetch
> and update plan, and needs some re factoring.
>
> Best Regards
>
>
>
>
> On Mon, Feb 24, 2014 at 10:12 PM, Ahsan Hadi <ahs...@en...>wrote:
>
>> Abbas,
>> Please give us an update on progress?
>>
>>
>> On Thu, Feb 20, 2014 at 3:38 PM, Abbas Butt <abb...@en...>wrote:
>>
>>>
>>>
>>>
>>> On Thu, Feb 20, 2014 at 3:25 PM, Ahsan Hadi <ahs...@en...
>>> > wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Wed, Feb 19, 2014 at 3:56 PM, Abbas Butt <
>>>> abb...@en...> wrote:
>>>>
>>>>> Lets do this
>>>>> 1. If the replicated table has a unique key defined , then use Mason's
>>>>> patch after testing and refinement if required.
>>>>> 2. If the replicated table has no key, then we can use cursors idea
>>>>> proposed by Ashutosh.
>>>>>
>>>>> Does every body agree?
>>>>>
>>>>
>>>> Yes.
>>>>
>>>> Can you provide a patch for the above before monday?
>>>>
>>>
>>> I will try my best to.
>>>
>>>
>>>>
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Feb 19, 2014 at 12:15 PM, Koichi Suzuki <koi...@gm...
>>>>> > wrote:
>>>>>
>>>>>> 2014-02-19 16:00 GMT+09:00 Ahsan Hadi <ahs...@en...>:
>>>>>> >
>>>>>> >
>>>>>> >
>>>>>> > On Tue, Feb 18, 2014 at 11:26 PM, Amit Khandekar
>>>>>> > <ami...@en...> wrote:
>>>>>> >>
>>>>>> >>
>>>>>> >>
>>>>>> >>
>>>>>> >> On 13 February 2014 11:54, Ashutosh Bapat
>>>>>> >> <ash...@en...> wrote:
>>>>>> >>>
>>>>>> >>> 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.
>>>>>> >>>
>>>>>> >>
>>>>>> >> Locking all rows doesn't look good especially because we are
>>>>>> looking for a
>>>>>> >> permanent long term solution. If we can come up with some other
>>>>>> solution
>>>>>> >> that avoids this, we better avoid this compromise. For a
>>>>>> replicated table
>>>>>> >> with 10000 rows, all concurrent updates will be serialized even if
>>>>>> they are
>>>>>> >> updating a different row.
>>>>>> >>
>>>>>> >> Other thing is datanode performance impact for ORDER BY all
>>>>>> columns,
>>>>>> >> especially with many large size columns. I had also mentioned
>>>>>> about ORDER BY
>>>>>> >> in approach A. I am not sure whether there is some kind of
>>>>>> optimization in
>>>>>> >> the sort, such as: if we find unique rows with the first n
>>>>>> columns, it does
>>>>>> >> not compare the rest of the columns.
>>>>>> >>
>>>>>> >> I think declaring cursors is a cool idea in general for DMLs but it
>>>>>> >> requires refactoring of DML planning, and also it requires ORDER
>>>>>> BY. There
>>>>>> >> is a concurrent update issue #398 for which we do require a
>>>>>> refactor of DML
>>>>>> >> handling. While doing that it will be clearer whether declaring
>>>>>> cursor is
>>>>>> >> really beneficial or if it's not feasible. For ORDER BY, again,
>>>>>> for long
>>>>>> >> term, we should have a primary key or an internal unique key so
>>>>>> that rows
>>>>>> >> can be ordered on that single column as against all columns. So
>>>>>> again, we
>>>>>> >> still are better of with a new system column.
>>>>>> >>
>>>>>> >>
>>>>>> >> As regards to approach C, if we find a way to uniquely generate a
>>>>>> new row
>>>>>> >> id independently, then the task of generating rowid will be pretty
>>>>>> >> lightweight. We won't require any other table to store it or
>>>>>> generate it.
>>>>>> >> The coordinator will generate it at each insert (both fqs and
>>>>>> non-fqs), or
>>>>>> >> may be datanodes themselves find a way to generate a new rowid
>>>>>> which is
>>>>>> >> always the same regardless of the datanode. A combination of gxid,
>>>>>> timestamp
>>>>>> >> and cmd id can be used to construct a unique rowid at the
>>>>>> coordinator.
>>>>>> >>
>>>>>> >> I think one action plan can be :
>>>>>> >> 1. Use Mason's patch and tweak it so that it needs very little
>>>>>> >> modification later on if and when we add the system rowid column.
>>>>>> >> 2. Check in the patch but let it not error out if the primary key
>>>>>> is not
>>>>>> >> there. This way we would at least make the replicated tables with
>>>>>> primary
>>>>>> >> keys work without data issues, but continue to work as it is now
>>>>>> for tables
>>>>>> >> without primary key.
>>>>>> >> 3. Lastly support the new system row id implementation, and do an
>>>>>> >> incremental change in Mason's checked in changes to use this id
>>>>>> instead of
>>>>>> >> primary key.
>>>>>> >>
>>>>>> >
>>>>>> > Sounds good but as i understand 3 is not targeted for 1.2?
>>>>>>
>>>>>> I agree on this too.   System column will benefit not only this, but
>>>>>> also WCO, more variety of the cursor, and Triggers.   I agree this is
>>>>>> targeted to 1.3 or later.
>>>>>>
>>>>>> Regards;
>>>>>> ---
>>>>>> Koichi Suzuki
>>>>>>
>>>>>> >
>>>>>> >>
>>>>>> >>
>>>>>> >>>
>>>>>> >>> 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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>>>>>> >>>> > Postgres-xc-developers mailing list
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>>>>>> >>>
>>>>>> >>>
>>>>>> >>> --
>>>>>> >>> Best Wishes,
>>>>>> >>> Ashutosh Bapat
>>>>>> >>> EnterpriseDB Corporation
>>>>>> >>> The Postgres Database Company
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>
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>>>>>> >
>>>>>> >
>>>>>> >
>>>>>> > --
>>>>>> > Ahsan Hadi
>>>>>> > Snr Director Product Development
>>>>>> > EnterpriseDB Corporation
>>>>>> > The Enterprise Postgres Company
>>>>>> >
>>>>>> > Phone: +92-51-8358874
>>>>>> > Mobile: +92-333-5162114
>>>>>> >
>>>>>> > Website: www.enterprisedb.com
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>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> --
>>>>> *Abbas*
>>>>>  Architect
>>>>>
>>>>> Ph: 92.334.5100153
>>>>>  Skype ID: gabbasb
>>>>> www.enterprisedb.co <http://www.enterprisedb.com/>m<http://www.enterprisedb.com/>
>>>>>
>>>>> *Follow us on Twitter*
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>>>>>
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Ahsan Hadi
>>>> Snr Director Product Development
>>>> EnterpriseDB Corporation
>>>> The Enterprise Postgres Company
>>>>
>>>> Phone: +92-51-8358874
>>>> Mobile: +92-333-5162114
>>>>
>>>> Website: www.enterprisedb.com
>>>> EnterpriseDB Blog: http://blogs.enterprisedb.com/
>>>> Follow us on Twitter: http://www.twitter.com/enterprisedb
>>>>
>>>> This e-mail message (and any attachment) is intended for the use of the
>>>> individual or entity to whom it is addressed. This message contains
>>>> information from EnterpriseDB Corporation that may be privileged,
>>>> confidential, or exempt from disclosure under applicable law. If you are
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>>>
>>>
>>>
>>> --
>>> --
>>> *Abbas*
>>>  Architect
>>>
>>> Ph: 92.334.5100153
>>>  Skype ID: gabbasb
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>>
>>
>>
>> --
>> Ahsan Hadi
>> Snr Director Product Development
>> EnterpriseDB Corporation
>> The Enterprise Postgres Company
>>
>> Phone: +92-51-8358874
>> Mobile: +92-333-5162114
>>
>> Website: www.enterprisedb.com
>> EnterpriseDB Blog: http://blogs.enterprisedb.com/
>> Follow us on Twitter: http://www.twitter.com/enterprisedb
>>
>> This e-mail message (and any attachment) is intended for the use of the
>> individual or entity to whom it is addressed. This message contains
>> information from EnterpriseDB Corporation that may be privileged,
>> confidential, or exempt from disclosure under applicable law. If you are
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>> copying of this communication is strictly prohibited. If you have received
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>
>
>
> --
> --
> *Abbas*
>  Architect
>
> Ph: 92.334.5100153
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>
> *Follow us on Twitter*
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>



-- 
-- 
*Abbas*
 Architect

Ph: 92.334.5100153
 Skype ID: gabbasb
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