Re: Patch: raise default for max_wal_segments to 1GB

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Josh Berkus <josh(at)agliodbs(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Venkata Balaji N <nag1010(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: Patch: raise default for max_wal_segments to 1GB
Date: 2015-03-03 18:37:32
Message-ID: 54F5FF6C.3020008@iki.fi
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On 03/03/2015 08:31 PM, Josh Berkus wrote:
> On 03/03/2015 10:29 AM, Heikki Linnakangas wrote:
>> On 03/03/2015 08:21 PM, Josh Berkus wrote:
>>> On 03/03/2015 10:15 AM, Josh Berkus wrote:
>>>> On 03/02/2015 11:25 PM, Heikki Linnakangas wrote:
>>>>> I propose that we remove the comment from max_wal_size, and also remove
>>>>> the "in milliseconds" from wal_receiver_timeout and
>>>>> autovacuum_vacuum_cost_delay.
>>>>
>>>> +1
>>>>
>>>
>>> Actually, let's be consistent about this. It makes no sense to remove
>>> unit comments from some settings which accept ms but not others.
>>>
>>> Do we want to remove unit comments from all settings which accept
>>> "MB,GB" or "ms,s,min"? There's more than a few. I'd be in favor of
>>> this, but seems like (a) it should be universal, and (b) its own patch.
>>
>> I think it's a good rule that if the commented-out default in the sample
>> file does not contain a unit, then the base unit is in the comment.
>> Otherwise it's not. For example:
>>
>> #shared_buffers = 32MB # min 128kB
>> # (change requires restart)
>>
>> The base unit is BLCKSZ, i.e. 8k, but usually people will usually use
>> MB/GB. And that is evident from the default value, 32MB, so there's no
>> need to mention it in the comment.
>>
>> #tcp_keepalives_idle = 0 # TCP_KEEPIDLE, in seconds;
>> # 0 selects the system default
>>
>> Here it's not obvious what the unit should be from the default itself.
>> So the comment says it's "in seconds".
>
> Sure. Although, do we take (s) for tcp_keepalives_idle? Or only an INT?

It's a "time unit", so you can say "10s" or "10000ms". If you don't
specify a unit, it implies seconds.

- Heikki

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