Thread: Stopping writes in master
Hi Debraj Manna,
You have to make your client as read only so that client can not write on the master.
Hope this helps..
You have to make your client as read only so that client can not write on the master.
Hope this helps..
On Thu, Jun 14, 2018 at 4:16 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:
HiIn a 3 node cluster with 1 master and 2 slaves with postgres 10.4 is there any configuration setting that will stop all writes to the master from the client. But the clients can read data from master and other slaves ?Thanks,
Hi Debraj Manna,
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.
ALTER DATABASE YOUR_DATABASE_NAME SET default_transaction_read_only = true;
Hope this helps..
Hope this helps..
On Thu, Jun 14, 2018 at 4:53 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:
Yes I want to switch the database to read-only mode. The existing connections should also be not able to write.On Thu 14 Jun, 2018, 4:37 PM Robert Zenz, <robert.zenz@sibvisions.com> wrote:Can existing connections be dropped or do they need to stay established? Also,
are you trying to switch the database to a read-only mode for backup purposes or
something different?
On 14.06.2018 12:46, Debraj Manna wrote:
> Hi
>
> In a 3 node cluster with 1 master and 2 slaves with postgres 10.4 is there
> any configuration setting that will stop all writes to the master from the
> client. But the clients can read data from master and other slaves ?
>
> Thanks,
>
Thanks Shreeyansh.
Can this be handled from the server side may be setting some config parameters and then restarting the master so that existing connections gets dropped and the new ones not able to write?
On Thu 14 Jun, 2018, 5:36 PM Shreeyansh Dba, <shreeyansh2014@gmail.com> wrote:
Hi Debraj Manna,
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.ALTER DATABASE YOUR_DATABASE_NAME SET default_transaction_read_only = true;
Hope this helps..On Thu, Jun 14, 2018 at 4:53 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:Yes I want to switch the database to read-only mode. The existing connections should also be not able to write.On Thu 14 Jun, 2018, 4:37 PM Robert Zenz, <robert.zenz@sibvisions.com> wrote:Can existing connections be dropped or do they need to stay established? Also,
are you trying to switch the database to a read-only mode for backup purposes or
something different?
On 14.06.2018 12:46, Debraj Manna wrote:
> Hi
>
> In a 3 node cluster with 1 master and 2 slaves with postgres 10.4 is there
> any configuration setting that will stop all writes to the master from the
> client. But the clients can read data from master and other slaves ?
>
> Thanks,
>
Hi Debraj Manna,
Yes, You may change some other parameters in config file except default_transaction_read_only=true and restart master.
But you can not set this default_transaction_read_only=true in the config file, because it will affect on whole database cluster means your cluster will go in read-only mode.
You can set this parameter at the session level to make particular database read-only. If you want to drop existing connections then reconnect the existing connections or restart the application if you can afford the downtime.
You can set this parameter at the session level to make particular database read-only. If you want to drop existing connections then reconnect the existing connections or restart the application if you can afford the downtime.
On Thu, Jun 14, 2018 at 7:16 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:
Thanks Shreeyansh.Can this be handled from the server side may be setting some config parameters and then restarting the master so that existing connections gets dropped and the new ones not able to write?On Thu 14 Jun, 2018, 5:36 PM Shreeyansh Dba, <shreeyansh2014@gmail.com> wrote:Hi Debraj Manna,
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.ALTER DATABASE YOUR_DATABASE_NAME SET default_transaction_read_only = true;
Hope this helps..On Thu, Jun 14, 2018 at 4:53 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:Yes I want to switch the database to read-only mode. The existing connections should also be not able to write.On Thu 14 Jun, 2018, 4:37 PM Robert Zenz, <robert.zenz@sibvisions.com> wrote:Can existing connections be dropped or do they need to stay established? Also,
are you trying to switch the database to a read-only mode for backup purposes or
something different?
On 14.06.2018 12:46, Debraj Manna wrote:
> Hi
>
> In a 3 node cluster with 1 master and 2 slaves with postgres 10.4 is there
> any configuration setting that will stop all writes to the master from the
> client. But the clients can read data from master and other slaves ?
>
> Thanks,
>
I can think of two other ways but the latter is more a pause than read-only. Neither are ideal solutions but hacks that may work depending on your needs.
1. If you’re restarting the server; then just make it a replia of nobody.
Con:
1. Requires database restart which could take a while depending on database activity
2. Truly is read only… i.e. no temp tables, etc.
i.e. Create a recovery.conf and restart the server… the database is truly read only.
recovery.conf:
standby_mode = 'on'
primary_conninfo = ‘host=nowhere'
2. Without restarting server; enable synchronous replication to nowhere and reload config.
Cons:
1. More of a pause than read-only
2. Clients can still write changes but will hang on commit (causing applications to hang).
3. Ctrl-c on a hanged session will actually commit the record on the master (oops)
Pro or Con depending on your view:
1. When releasing the synchronous setup to nowhere; hung sessions will carry on with their commit.
postgres.conf:
synchronous_standby_names = ‘1 (nowhere)’
If you trust your clients; then setting the default transaction state and killing the sessions forcing a reconnect might be the best solution like has already been suggested; however, if you dealing with end users they can change their session transaction level back.
On Jun 14, 2018, at 9:46 AM, Debraj Manna <subharaj.manna@gmail.com> wrote:Thanks Shreeyansh.Can this be handled from the server side may be setting some config parameters and then restarting the master so that existing connections gets dropped and the new ones not able to write?On Thu 14 Jun, 2018, 5:36 PM Shreeyansh Dba, <shreeyansh2014@gmail.com> wrote:Hi Debraj Manna,
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.ALTER DATABASE YOUR_DATABASE_NAME SET default_transaction_read_only = true;
Hope this helps..On Thu, Jun 14, 2018 at 4:53 PM, Debraj Manna <subharaj.manna@gmail.com> wrote:Yes I want to switch the database to read-only mode. The existing connections should also be not able to write.On Thu 14 Jun, 2018, 4:37 PM Robert Zenz, <robert.zenz@sibvisions.com> wrote:Can existing connections be dropped or do they need to stay established? Also,
are you trying to switch the database to a read-only mode for backup purposes or
something different?
On 14.06.2018 12:46, Debraj Manna wrote:
> Hi
>
> In a 3 node cluster with 1 master and 2 slaves with postgres 10.4 is there
> any configuration setting that will stop all writes to the master from the
> client. But the clients can read data from master and other slaves ?
>
> Thanks,
>
Yeah forgot to send to thread
Thursday, June 14, 2018 11:42 AMI did think about it after I hit sent; but it really doing to depend on if they setup all permissions using roles; which is good practice to do.Did you just mean to send this to me? You should suggest it to thread as an option.Thursday, June 14, 2018 11:38 AMI wonder why nobody suggested access control changes to accomplish the read only. That is change permissions on some or all users that can log into the database and adjust them accordingly.
Regards,
Michael Vitale
Thursday, June 14, 2018 11:20 AMI can think of two other ways but the latter is more a pause than read-only. Neither are ideal solutions but hacks that may work depending on your needs.1. If you’re restarting the server; then just make it a replia of nobody.Con:1. Requires database restart which could take a while depending on database activity2. Truly is read only… i.e. no temp tables, etc.i.e. Create a recovery.conf and restart the server… the database is truly read only.recovery.conf:standby_mode = 'on'primary_conninfo = ‘host=nowhere'2. Without restarting server; enable synchronous replication to nowhere and reload config.Cons:1. More of a pause than read-only2. Clients can still write changes but will hang on commit (causing applications to hang).3. Ctrl-c on a hanged session will actually commit the record on the master (oops)Pro or Con depending on your view:1. When releasing the synchronous setup to nowhere; hung sessions will carry on with their commit.postgres.conf:synchronous_standby_names = ‘1 (nowhere)’If you trust your clients; then setting the default transaction state and killing the sessions forcing a reconnect might be the best solution like has already been suggested; however, if you dealing with end users they can change their session transaction level back.Thursday, June 14, 2018 9:46 AMThanks Shreeyansh.Can this be handled from the server side may be setting some config parameters and then restarting the master so that existing connections gets dropped and the new ones not able to write?Thursday, June 14, 2018 8:06 AMHi Debraj Manna,
Yes,You can make the database read only as well just by setting the below parameter is equal to true at the session level.But you need reconnect your existing connections.ALTER DATABASE YOUR_DATABASE_NAME SET default_transaction_read_only = true;
Hope this helps..