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Thread: max_wal_size and wal_keep_size

max_wal_size and wal_keep_size

From
"James Pang (chaolpan)"
Date:

Hi,

It’s PGv13,  what’s relationship between max_wal_size and wal_keep_size ?  For example, wal_keep_size=200GB(to keep enough wal on disk pg_wal) ,   what’s best value for max_wal_size ?   we want to usage max_wal_size to control checkpoint .

 

Thanks,

 

James

Re: max_wal_size and wal_keep_size

From
Jeff Janes
Date:
On Sun, Aug 28, 2022 at 8:46 AM James Pang (chaolpan) <chaolpan@cisco.com> wrote:

Hi,

It’s PGv13,  what’s relationship between max_wal_size and wal_keep_size ?  For example, wal_keep_size=200GB(to keep enough wal on disk pg_wal) ,   what’s best value for max_wal_size ?   we want to usage max_wal_size to control checkpoint .


The settings are independent.  Do you think your checkpoints are occurring too often or not often enough?  (After an unclean shutdown does it take too long for the system to come back up again?)

Cheers,

Jeff


RE: max_wal_size and wal_keep_size

From
"James Pang (chaolpan)"
Date:

We want keep more wal to give more room for data replication, in case of some delay , and need old wal data. So wan to set wal_keep_size , and want to increase max_wal-size a lot to make max_wal_size > wal_keep_size (it may > 1TB).

 

James

 

From: Jeff Janes <jeff.janes@gmail.com>
Sent: Sunday, August 28, 2022 10:53 PM
To: James Pang (chaolpan) <chaolpan@cisco.com>
Cc: pgsql-admin@lists.postgresql.org
Subject: Re: max_wal_size and wal_keep_size

 

On Sun, Aug 28, 2022 at 8:46 AM James Pang (chaolpan) <chaolpan@cisco.com> wrote:

Hi,

It’s PGv13,  what’s relationship between max_wal_size and wal_keep_size ?  For example, wal_keep_size=200GB(to keep enough wal on disk pg_wal) ,   what’s best value for max_wal_size ?   we want to usage max_wal_size to control checkpoint .

 

The settings are independent.  Do you think your checkpoints are occurring too often or not often enough?  (After an unclean shutdown does it take too long for the system to come back up again?)

 

Cheers,

 

Jeff

 

 

Re: max_wal_size and wal_keep_size

From
Laurenz Albe
Date:
On Tue, 2022-08-30 at 08:29 +0000, James Pang (chaolpan) wrote:
> We want keep more wal to give more room for data replication, in case of some delay ,
> and need old wal data. So wan to set wal_keep_size , and want to increase
> max_wal-size a lot to make max_wal_size > wal_keep_size (it may > 1TB).

The two parameters are independent:
- "max_wal_size" does *not* determine the maximum WAL size, but how much
  WAL can be produced before the next checkpoint is triggered.
- "wal_keep_size" determines how much old WAL is kept around.

Set "wal_keep_size" and leave "max_wal_size" unchanged.

Or even better, use a replication slot.

Yours,
Laurenz Albe
-- 
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