Re: Protect syscache from bloating with negative cache entries

On Sat, Jan 14, 2017 at 9:36 AM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> On 01/14/2017 12:06 AM, Andres Freund wrote:
>> On 2017-01-13 17:58:41 -0500, Tom Lane wrote:
>>>
>>> But, again, the catcache isn't the only source of per-process bloat
>>> and I'm not even sure it's the main one. A more holistic approach
>>> might be called for.
>>
>> It'd be helpful if we'd find a way to make it easy to get statistics
>> about the size of various caches in production systems. Right now
>> that's kinda hard, resulting in us having to make a lot of
>> guesses...
>
> What about a simple C extension, that could inspect those caches? Assuming
> it could be loaded into a single backend, that should be relatively
> acceptable way (compared to loading it to all backends using
> shared_preload_libraries).

This extension could do a small amount of work on a portion of the
syscache entries at each query loop, still I am wondering if that
would not be nicer to get that in-core and configurable, which is
basically the approach proposed by Horiguchi-san. At least it seems to
me that it has some merit, and if we could make that behavior
switchable, disabled by default, that would be a win for some class of
applications. What do others think?
--
Michael