Re: Synchronize the dump with a logical slot with --snapshot

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From: Durgamahesh Manne <[email protected]>
To: Justin <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Greg Sabino Mullane <[email protected]>
Cc: Koichi Suzuki <[email protected]>
Subject: Re: Synchronize the dump with a logical slot with --snapshot
Date: Sun, 29 Sep 2024 00:22:39 +0530
Message-ID: <CAJCZkoK8jmADFWKYkk8GUvZSfVbf=Zkk6EHomnPhHvayTYoWaQ@mail.gmail.com> (raw)
In-Reply-To: <CALL-XeNd=8v7BF1RyamWK7ur9rjbbC40A3N8GFjBC+ZX3azeVQ@mail.gmail.com>
References: <CAJCZkoJ_=jAf+HVh8_fGRw-C+HAD7M0k+HKD=4Bvc1KcbZVnfA@mail.gmail.com>
	<CAJCZkoLGxyNESVWD5uPwWcA=hye44LQ9=v4=TJDA0s-Rhd04jg@mail.gmail.com>
	<CAJCZkoKi3SQ0jKqQFDuOTfeE1XRmtUqtGjCB+DTacpwEuG5MQQ@mail.gmail.com>
	<CALL-XeNd=8v7BF1RyamWK7ur9rjbbC40A3N8GFjBC+ZX3azeVQ@mail.gmail.com>

Hi justin

I raised question based on the reference link
https://opensource-db.com/unlocking-initial-sync-for-logical-replication-in-aws-rds-for-postgresql/
  .. you can also go through it to see the steps
This worked on postgres 10version but on postgres 14 I can go through the
info you provided to implement the same

Thanks for your valuable information

Regards,
Durga Mahesh


On Sat, 28 Sept, 2024, 23:10 Justin, <[email protected]> wrote:

>
>
> On Sat, Sep 28, 2024 at 1:04 AM Durgamahesh Manne <
> [email protected]> wrote:
>
>> Hi Team
>>
>> Can anyone respond to my question from respected team members ?
>>
>> Durga Mahesh
>>
>> On Thu, Sep 26, 2024 at 2:23 AM Durgamahesh Manne <
>> [email protected]> wrote:
>>
>>> Hi Team
>>>
>>> --snapshot=snapshotname
>>> (Use the specified synchronized snapshot when making a dump of the
>>> database
>>>
>>> This option is useful when needing to synchronize the dump with a
>>> logical replication slot) as per the pgdg
>>>
>>> How do we synchronize the dump with a logical replication slot with
>>> --snapshot?
>>>
>>> I am using the postgresql 14 version which supports only
>>> pg_create_logical_replication_slot. How to generate a internal snapshot
>>> with it ?
>>>
>>> Below CREATE_REPLICAION_SLOT not supported by postgresql 14
>>>
>>> example osdb_lsr=# CREATE_REPLICATION_SLOT lsr_sync_01 LOGICAL pgoutput;
>>>   slot_name | consistent_point | snapshot_name | output_plugin
>>> -------------+------------------+---------------------+---------------
>>>  lsr_sync_01 | 0/C000110 | 00000003-00000002-1 | pgoutput
>>>
>>> Regards,
>>>
>>> Durga Mahesh
>>>
>>>
>>>
>>> On Fri, 20 Sept, 2024, 01:27 Durgamahesh Manne, <
>>> [email protected]> wrote:
>>>
>>>> Hi Team
>>>>
>>>> --snapshot=*snapshotname*
>>>>
>>>> (Use the specified synchronized snapshot when making a dump of the
>>>> database
>>>>
>>>> This option is useful when needing to synchronize the dump with a
>>>> logical replication slot) as per the pgdg
>>>>
>>>> How do we synchronize the dump with a logical replication slot
>>>> with --snapshot?
>>>>
>>>> I am using the postgresql 14 version which supports only
>>>> pg_create_logical_replication_slot. How to generate a snapshot with it ?
>>>>
>>>> Below CREATE_REPLICAION_SLOT not supported by postgresql 14
>>>>
>>>> example osdb_lsr=# CREATE_REPLICATION_SLOT lsr_sync_01 LOGICAL pgoutput;
>>>>   slot_name  | consistent_point |    snapshot_name    | output_plugin
>>>> -------------+------------------+---------------------+---------------
>>>>  lsr_sync_01 | 0/C000110        | 00000003-00000002-1 | pgoutput
>>>>
>>>> Regards,
>>>>
>>>> Durga Mahesh
>>>>
>>>
>
> Hi Durgamahesh,
>
> I am not sure what you are after with matching pg_dump and replication
> slot together unless you are trying to get a dump to handle the initial
> data sync. There is not a benefit to doing that as the WAL is going to
> build up on the publisher...
>
> You have to create a snapshot using the export function
>
> https://www.postgresql.org/docs/current/sql-set-transaction.html
>
>
> https://www.postgresql.org/docs/17/functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION
>
> Then you can create the logical replication slot with using that slotname
> option
>
> https://www.postgresql.org/docs/17/sql-createsubscription.html#SQL-CREATESUBSCRIPTION-PARAMS-WITH-SL...
> and no sync option.
>
> Then you tell pg_dump to use that snapshot name snapshot with this option
> --snapshot=snapshotname
>
> https://www.postgresql.org/docs/current/app-pgdump.html
>
> Once pg_restore is done on the destination , you can create a subscription
> using that slotname option probably and specify copy_data = false.
>
> Keep in mind the WAL will build up during this process,  not sure what the
> benefit would be just allowing logical replication to do the initial sync.
>
>
> Thanks
> Justin
>
>

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