Re: PgBackRest PTR recovery: After table drop to get dropped state

Hi

On Fri, Aug 2, 2024 at 1:28 PM KK CHN <kkchn(dot)in(at)gmail(dot)com> wrote:

> Thank you for shedding light on this.
>
> On Thu, Aug 1, 2024 at 4:04 PM Mateusz Henicz <mateuszhenicz(at)gmail(dot)com>
> wrote:
>
>> When you are performing PITR you need to configure a timestamp before
>> your last committed transaction. In your case you provided timestamp after
>> your last commit.
>>
>>
>
> I am trying to understand this concept and correct me if I am wrong
> If I do
>
> STEPS:
> 1. Noting down the time stamp just before my table drop, then
> 2. Drop a table, then
> 3. Taking the incremental backup after this table drop on Repo server,
> Then
>
When you take a back and checkpoint is called which will update the data
files and till that time you now dont need the WAL Files as they are
already written on Data Files and are part of the backp.

How PITR works is
1. You take a backup (full/incremental)
2. Make changes in the data
3. Note down all the timestamps per the transactions as you need them
4. Now if you want to restore,what you will do is to give the required
timestamp with the required backup
This will restore the backup and then replay the WAL files as per your
given timestamp

I hope this clarifies

Regards
Kashif Zeeshan

> 4. If I do a PITR, with --target = timestamp noted in step1 and --set
> = the incr backup taken in step3
>
> Then if perform a PITR restore by pgbackrest in step4 will it succeed
> or fail theoretically ?
>
> Thanks,
> Krishane
>
>
> When postgtes is restoring until a specified point, it restores a
>> transaction from WAL, and checking if next transaction is before or after
>> said timestamp. If it is before it will replay it and check next
>> transaction. Until next transaction is after configured timestamp.
>> If there is no transaction after your current timestamp in current WAL,
>> postgres will try to restore next WAL from archive. And since there is no
>> next WAL, and your timestamp is past latest committed transaction, it is
>> unable to continue, because it does not know if there should be any other
>> transaction replayed or not.
>>
>> Just perform some other actions after you note down the timestamp after
>> drop table. Create another one, insert some data, do whatever to have
>> another transaction in WALs.
>>
>> Cheers,
>> Mateusz
>>
>> czw., 1 sie 2024 o 12:23 KK CHN <kkchn(dot)in(at)gmail(dot)com> napisał(a):
>>
>>> The logs are here.
>>>
>>> https://pastecode.io/s/s5dp8ur1
>>>
>>>
>>>
>>> On Thu, Aug 1, 2024 at 3:30 PM Kashif Zeeshan <kashi(dot)zeeshan(at)gmail(dot)com>
>>> wrote:
>>>
>>>> Hi
>>>>
>>>> On Thu, Aug 1, 2024 at 2:54 PM KK CHN <kkchn(dot)in(at)gmail(dot)com> wrote:
>>>>
>>>>> List,
>>>>>
>>>>> *Not working (start EPAS server always fails):*
>>>>>
>>>>> 1. Testing PTR using PgBackRest(2.52.1) on RHEL9 EPAS-16, and RHEL9
>>>>> ( Repo Server)
>>>>>
>>>>> When I do a PTR
>>>>>
>>>>> 1. After doing a table drop and then
>>>>> 2. Noting down the time stamp and then
>>>>> 3. Taking an incremental backup in hope that If I do a restore from
>>>>> this incr Backup, that won't contain the dropped table.
>>>>> 4. Correct me if I am conceptually wrong here.
>>>>> 5. I am *never *successful in restoring the EPAS server in this
>>>>> scenario.
>>>>>
>>>>>
>>>>> *I know the following will work for me, w*hy not the above one if I
>>>>> really want that state of cluster also ?
>>>>>
>>>>> *This is Working. *
>>>>> 1. Create table
>>>>> 2. Noting down the timestamp
>>>>> 3. Taking incremental backup on RepoServer.
>>>>> 4. drop the created table .
>>>>> 5. Then stop the EPAS server and do a PTR, by the --set=step 3 incr
>>>>> backup and target= step 2 time stamp .. It finished the pgaback restore
>>>>> and promote command
>>>>> 6. I am able to start back the EPAS server and see the dropped table
>>>>> recovered there.
>>>>>
>>>>> But If I want a PTR as in the first section it fails.. Why ?
>>>>>
>>>>> Thank you,
>>>>> Krishane
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> *What I have done and results obtained: *
>>>>>
>>>>> Created a table important_table4 in my EPAS and note down the time
>>>>> after creation of this table it is ( t1 : "01-AUG-24
>>>>> 14:08:32.447796+05:30" )
>>>>>
>>>>> Then I performed an Incremental backup (incr backup:
>>>>> 20240729-160137F_20240801-141148I )
>>>>> timestamp start/stop: 2024-08-01 14:11:48+05:30 / 2024-08-01
>>>>> 14:11:52+05:30
>>>>>
>>>>>
>>>>> Now I dropped the table table4 from the EPAS and noted down the time
>>>>>
>>>>>
>>>>> I want to restore the table4,, so I stopped EPAS and executed
>>>>>
>>>>> $ sudo -u enterprisedb pgbackrest --stanza=Demo_Repo --delta
>>>>> --set=20240729-160137F_20240801-141148I --target-timeline=current
>>>>> --type=time --target="01-AUG-24 14:08:32.447796+05:30"
>>>>> --target-action=promote restore
>>>>>
>>>>> IT WORKS AS EXPECTED .. after restarting the EPAS I am able to get the
>>>>> important_table4 back.
>>>>>
>>>>> root(at)service01 ~]# sudo -u enterprisedb psql edb
>>>>> psql (16.3.0)
>>>>> Type "help" for help.
>>>>>
>>>>> edb=# \dt
>>>>> List of relations
>>>>> Schema | Name | Type | Owner
>>>>> --------+------------------+-------+--------------
>>>>> public | important_table | table | enterprisedb
>>>>> public | important_table2 | table | enterprisedb
>>>>> public | important_table3 | table | enterprisedb
>>>>> public | important_table4 | table | enterprisedb
>>>>> (4 rows)
>>>>>
>>>>> SO all works fine !!!! .
>>>>>
>>>>>
>>>>> *But Now the PROBLEM Statement. *
>>>>>
>>>>> *1. I am dropping the table table 4 again *
>>>>> edb=# \q
>>>>> [root(at)service01 ~]# sudo -u enterprisedb psql -c "begin; drop table
>>>>> important_table4; commit;" edb
>>>>> BEGIN
>>>>> DROP TABLE
>>>>> COMMIT
>>>>> *2 . [root(at)service01 ~]#* sudo -u enterprisedb psql -Atc "select
>>>>> current_timestamp" edb 01-AUG-24 14:23:22.085076 +05:30
>>>>> Noting the time as : (01-AUG-24 14:23:22.085076 +05:30 )
>>>>>
>>>>> 3. Now I am performing an incremental backup after step 2 on REPO
>>>>> SErver ( Hoping that this latest INCR Backup is without dropped
>>>>> important_table4, so that a recovery of the cluster shouldn't show the
>>>>> table4 again. )
>>>>>
>>>>> incr backup details. : 20240729-160137F_20240801-142433I
>>>>> timestamp start/stop*: 2024-08-01 14:24:33+05:30 /
>>>>> 2024-08-01 14:24:36+05:30*
>>>>>
>>>>> 4. Now I want to test the database recovery after dropping the table4
>>>>> in step1 to verify that my EPAS restores from the backup in step 3 and time
>>>>> stamp (01-AUG-24 14:23:22.085076 +05:30, so that the restored EPAS
>>>>> cluster doesn't contain the important_table4.
>>>>>
>>>>> 5. $ sudo -u enterprisedb pgbackrest --stanza=Demo_Repo --delta
>>>>> --set=20240729-160137F_20240801-142433I --target-timeline=current
>>>>> --type=time --target="01-AUG-24 14:23:22.085076+05:30"
>>>>> --target-action=promote restore
>>>>> ------------
>>>>> -------------
>>>>> INFO: restore command end: completed successfully (1035ms)
>>>>>
>>>>> *ISSUE: I am unable to get the EPAS Server* in running state after
>>>>> step 5
>>>>>
>>>>> *What am I doing wrong ? OR am I conceptually wrong ?*
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> OUTPUT on executing step 5.
>>>>>
>>>>> [root(at)service01 ~]# sudo -u enterprisedb pgbackrest
>>>>> --stanza=Demo_Repo --delta --set=20240729-160137F_20240801-142433I
>>>>> --target-timeline=current --type=time --target="01-AUG-24
>>>>> 14:23:22.085076+05:30" --target-action=promote restore
>>>>>
>>>>> 2024-08-01 14:30:03.535 P00 INFO: restore command begin 2.52.1:
>>>>> --delta --exec-id=82738-b5fe7415 --log-level-console=info
>>>>> --log-level-file=debug --pg1-path=/var/lib/edb/as16/data
>>>>> --pg-version-force=16 --repo1-host=10.10.20.7 --repo1-host-user=postgres
>>>>> --set=20240729-160137F_20240801-142433I --stanza=Demo_Repo
>>>>> --target="01-AUG-24 14:23:22.085076+05:30" --target-action=promote
>>>>> --target-timeline=current --type=time
>>>>> 2024-08-01 14:30:03.880 P00 INFO: repo1: restore backup set
>>>>> 20240729-160137F_20240801-142433I, recovery will start at 2024-08-01
>>>>> 14:24:33
>>>>> 2024-08-01 14:30:03.881 P00 INFO: remove invalid files/links/paths
>>>>> from '/var/lib/edb/as16/data'
>>>>> 2024-08-01 14:30:04.567 P00 INFO: write updated
>>>>> /var/lib/edb/as16/data/postgresql.auto.conf
>>>>> 2024-08-01 14:30:04.569 P00 INFO: restore global/pg_control
>>>>> (performed last to ensure aborted restores cannot be started)
>>>>> 2024-08-01 14:30:04.569 P00 INFO: restore size = 75.9MB, file total
>>>>> = 2171
>>>>> 2024-08-01 14:30:04.569 P00 INFO: restore command end: completed
>>>>> successfully (1035ms)
>>>>> *[root(at)service01 ~]# systemctl start edb-as-16.service*
>>>>>
>>>>> *Now If I check the server status : Its dead *
>>>>>
>>>>> [root(at)service01 ~]# systemctl status edb-as-16.service
>>>>> × edb-as-16.service - EDB Postgres Advanced Server 16
>>>>> Loaded: loaded (/etc/systemd/system/edb-as-16.service; disabled;
>>>>> preset: disabled)
>>>>> *Active: failed* (Result: exit-code) since Thu 2024-08-01
>>>>> 14:30:58 IST; 4s ago
>>>>> Duration: 228ms
>>>>> Process: 82752
>>>>> ExecStartPre=/usr/edb/as16/bin/edb-as-16-check-db-dir ${PGDATA}
>>>>> (code=exited, status=0/SUCCESS)
>>>>> Process: 82757 ExecStart=/usr/edb/as16/bin/edb-postgres -D
>>>>> ${PGDATA} (code=exited, status=1/FAILURE)
>>>>> Main PID: 82757 (code=exited, status=1/FAILURE)
>>>>> CPU: 325ms
>>>>>
>>>>> Aug 01 14:30:56 service01 systemd[1]: Starting EDB Postgres Advanced
>>>>> Server 16...
>>>>> Aug 01 14:30:56 service01 edb-postgres[82757]: 2024-08-01 14:30:56 IST
>>>>> LOG: redirecting log output to logging collector process
>>>>> Aug 01 14:30:56 rservice01 edb-postgres[82757]: 2024-08-01 14:30:56
>>>>> IST HINT: Future log output will appear in directory "log".
>>>>> Aug 01 14:30:58 service01 systemd[1]: Started EDB Postgres Advanced
>>>>> Server 16.
>>>>> Aug 01 14:30:58 service01 systemd[1]: edb-as-16.service: Main process
>>>>> exited, code=exited, status=1/FAILURE
>>>>> Aug 01 14:30:58 service01 systemd[1]: edb-as-16.service: Killing
>>>>> process 82758 (edb-postgres) with signal SIGKILL.
>>>>> A*ug 01 14:30:58 service01 systemd[1]: edb-as-16.service: Failed with
>>>>> result 'exit-code'.*
>>>>> [root(at)service01 ~]#
>>>>>
>>>>> Any hints/guidance most welcome.
>>>>>
>>>>> Can you please share the DB Server log as it contains the exact error
>>>> which is causing the server not to start.
>>>>
>>>> Thanks
>>>>
>>>