Subject: Re: Out of memory error on automatic vacuum
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-performance@lists.postgresql.org
References: <a5c8d612-693e-1546-5cbf-6d928287bdc6@zunibal.com>
 <20191118122528.45k3jpgaxevsyser@development>
 <c59d5d5c-e629-22e4-851c-dd74f6d3c6ec@zunibal.com>
 <20191118141605.4mmynff64c5prxgf@development>
From: Ekaterina Amez <ekaterina.amez@zunibal.com>
Message-ID: <b5c70ce2-e1d8-dfe3-72b0-4164697db488@zunibal.com>
Date: Mon, 18 Nov 2019 15:46:03 +0100
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El 18/11/19 a las 15:16, Tomas Vondra escribió:
>
> Not sure I understand. Whenever PostgreSQL process needs memory it
> requests it from the kernel by calling malloc(), and the amount of
> availabe RAM is limited.  So when kernel can't provide more memory,
> it returns NULL.
>
Understood.

>
> If it finished a couple of minutes before, it's unlikely to be the
> related. But hard to say, without knowing the details.

Yeah, I thought the same but for me is too much coincidence and is 
suspicious (or at least a thing to have in mind).


> No, that's just one of the memory contexts (they form a tree), using
> only 1kB of memory. What matters is the "grand total"
>
> Grand total: 1009356 bytes in 130 blocks; 436888 free (72 chunks);
> 572468 used
>
> which is ~1MB.
>
OK, in my lack of knowledge I was understanding "memory context" as the 
whole message.


> Another thing you might do is adding a swap (if you don't have one
> already), as a safety.
>
>
Excuse my ignorance but... swap? You mean some mechanism that prevents 
server to be unavailable by having a second instance running but not 
accesible and changing from one to the other when the main fails? (It's 
the best way I find to describe it, as I don't usually speak/write english).

Thanks for your time.