Subject: Re: effective_cache_size
To: Bruce Momjian <bruce@momjian.us>, nat@makarevitch.org,
 pgsql-docs@lists.postgresql.org
References: <153685164808.22334.15432535018443165207@wrigleys.postgresql.org>
 <20181011174849.GC7807@momjian.us> <20181016153820.GD31154@momjian.us>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
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Organization: 2ndQuadrant
Message-ID: <369ec766-b947-51bd-4dad-6fb9e026439f@2ndquadrant.com>
Date: Mon, 5 Nov 2018 12:50:01 +0100
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On 16/10/2018 17:38, Bruce Momjian wrote:
> diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
> index 2317e8b..e471d7f 100644
> --- a/src/backend/utils/misc/guc.c
> +++ b/src/backend/utils/misc/guc.c
> @@ -2987,10 +2987,9 @@ static struct config_int ConfigureNamesInt[] =
>  
>  	{
>  		{"effective_cache_size", PGC_USERSET, QUERY_TUNING_COST,
> -			gettext_noop("Sets the planner's assumption about the size of the disk cache."),
> -			gettext_noop("That is, the portion of the kernel's disk cache that "
> -						 "will be used for PostgreSQL data files. This is measured in disk "
> -						 "pages, which are normally 8 kB each."),
> +			gettext_noop("Sets the planner's assumption about the size of the data cache."),
> +			gettext_noop("That is, the size of the cache used for PostgreSQL data files. "
> +						 "This is measured in disk pages, which are normally 8 kB each."),
>  			GUC_UNIT_BLOCKS,
>  		},
>  		&effective_cache_size,

This change completely loses the context that this is the kernel's/host
system's memory size.  What is "data cache"?  I think this is a bad
change.  I know it's confusing, but the old description at least had
some basis in terms that are known to the user.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services