Thread: The behavior of CheckRequiredParameterValues()
Hi all, I had doubts regarding behavior of CheckRequiredParameterValues() function. I could not start standby server which is created by pg_basebackup with following scenario. 1. Start the master server with 'wal_level = archve' , 'hot_standby = on' and other settings of replication. 2. Create the standby server from the master server by using pg_basebackup. 3. Change the wal_level value of both master and standby server to 'hot_standby'. 4. Restarting the master server. 5. Starting the standby server. In #5, I got following error even if I set wal_level to 'hot_standby'. FATAL: hot standby is not possible because wal_level was not set to "hot_standby" or higher on the master server I tried to investigate this behaviour. Currently CheckRequiredParameterValues() function uses wal_level value which is got from ControlFile when comparing between wal_level and WAL_LEVEL_HOT_STANDBY as following code. xlog.c:6177if (ControlFile->wal_level < WAL_LEVEL_HOT_STANDBY) ereport(ERROR, (errmsg("hot standby is not possiblebecause wal_level was not So we have to start and stop standby server with changed wal_level(i.g., hot_standby) if we want to enable hot standby. In this case, I think that the standby server didn't need to confirm wal_level value of ControlFile. I think that it should confirm value which is written in postgreql.conf. I might be missing something. Please let me know that. Regards, ------- Sawada Masahiko
On Wed, Mar 5, 2014 at 4:09 AM, Sawada Masahiko <sawada.mshk@gmail.com> wrote:
Hi all,
I had doubts regarding behavior of CheckRequiredParameterValues() function.
I could not start standby server which is created by pg_basebackup
with following scenario.
1. Start the master server with 'wal_level = archve' , 'hot_standby =
on' and other settings of replication.
2. Create the standby server from the master server by using pg_basebackup.
3. Change the wal_level value of both master and standby server to
'hot_standby'.
4. Restarting the master server.
5. Starting the standby server.
In #5, I got following error even if I set wal_level to 'hot_standby'.
FATAL: hot standby is not possible because wal_level was not set to
"hot_standby" or higher on the master server
I tried to investigate this behaviour.
Currently CheckRequiredParameterValues() function uses wal_level value
which is got from ControlFile when comparing between wal_level and
WAL_LEVEL_HOT_STANDBY as following code.
xlog.c:6177
if (ControlFile->wal_level < WAL_LEVEL_HOT_STANDBY)
ereport(ERROR,
(errmsg("hot standby is not possible because wal_level was not
So we have to start and stop standby server with changed
wal_level(i.g., hot_standby) if we want to enable hot standby.
In this case, I think that the standby server didn't need to confirm
wal_level value of ControlFile.
I think that it should confirm value which is written in postgreql.conf.
The snapshot of running transaction information is written to WAL only when the wal_level is set to 'hot_standby'.
This information is required on the standby side to recreate the running transactions.
Regards,
Hari Babu
Fujitsu Australia
On Wed, Mar 5, 2014 at 2:09 AM, Sawada Masahiko <sawada.mshk@gmail.com> wrote: > > xlog.c:6177 > if (ControlFile->wal_level < WAL_LEVEL_HOT_STANDBY) > ereport(ERROR, > (errmsg("hot standby is not possible because wal_level was not > > So we have to start and stop standby server with changed > wal_level(i.g., hot_standby) if we want to enable hot standby. > In this case, I think that the standby server didn't need to confirm > wal_level value of ControlFile. > I think that it should confirm value which is written in postgreql.conf. > I think checking it from the control file on a standby in recovery means that we should confirm if the *wal_level with which the WAL was generated* is sufficient to now become a hot standby after recovery finishes. -- Amit
On Wed, Mar 5, 2014 at 12:07 PM, Amit Langote <amitlangote09@gmail.com> wrote: > On Wed, Mar 5, 2014 at 2:09 AM, Sawada Masahiko <sawada.mshk@gmail.com> wrote: > >> >> xlog.c:6177 >> if (ControlFile->wal_level < WAL_LEVEL_HOT_STANDBY) >> ereport(ERROR, >> (errmsg("hot standby is not possible because wal_level was not >> >> So we have to start and stop standby server with changed >> wal_level(i.g., hot_standby) if we want to enable hot standby. >> In this case, I think that the standby server didn't need to confirm >> wal_level value of ControlFile. >> I think that it should confirm value which is written in postgreql.conf. >> > > I think checking it from the control file on a standby in recovery > means that we should confirm if the *wal_level with which the WAL was > generated* is sufficient to now become a hot standby after recovery > finishes. > Sorry, should have said: *become a hot standby after recovery reaches a consistent state -- Amit
On Wed, Mar 5, 2014 at 5:13 PM, Amit Langote <amitlangote09@gmail.com> wrote: > On Wed, Mar 5, 2014 at 12:07 PM, Amit Langote <amitlangote09@gmail.com> wrote: >> On Wed, Mar 5, 2014 at 2:09 AM, Sawada Masahiko <sawada.mshk@gmail.com> wrote: >> >>> >>> xlog.c:6177 >>> if (ControlFile->wal_level < WAL_LEVEL_HOT_STANDBY) >>> ereport(ERROR, >>> (errmsg("hot standby is not possible because wal_level was not >>> >>> So we have to start and stop standby server with changed >>> wal_level(i.g., hot_standby) if we want to enable hot standby. >>> In this case, I think that the standby server didn't need to confirm >>> wal_level value of ControlFile. >>> I think that it should confirm value which is written in postgreql.conf. >>> >> >> I think checking it from the control file on a standby in recovery >> means that we should confirm if the *wal_level with which the WAL was >> generated* is sufficient to now become a hot standby after recovery >> finishes. >> > > Sorry, should have said: > *become a hot standby after recovery reaches a consistent state > Thank you for explain! I understood it! Regards, ------- Sawada Masahiko