Re: [External] Re: Separate volumes

That makes sense. The person who told me this was very experienced with
Oracle but was a PG novice.
-Ed

Ed Behn | Senior Systems Engineer | Avionics

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On Mon, Apr 6, 2020 at 3:33 PM MichaelDBA <MichaelDBA(at)sqlexec(dot)com> wrote:

> Hi Steve,
>
> Coming from oracle land, tablespaces play a bigger role than they do in PG
> land. In PG land, they can control the mapping of tables/indexes to faster
> or slower devices. By separating a table's tablespace from its index
> tablespace, you may get more parallel I/O. They also allow for flexibility
> in setting pg config parameters per tablespace:
>
> alter tablespace mytablespace set ( seq_page_cost=0.5, random_page_cost=0.5 );
>
> But they also can be a headache in managing stuff. For instance, all
> replicas must have the same directory structure and symlinks.
>
> Regards,
> Michael Vitale
>
>
>
> Steve Midgley wrote on 4/6/2020 1:11 PM:
>
>
>
> On Mon, Apr 6, 2020 at 9:42 AM Erik Brandsberg <erik(at)heimdalldata(dot)com>
> wrote:
>
>> With SSD and it's random IO performance, I doubt that this advice would
>> apply as much, and adds complexity to your configuration and management.
>> In particular if you use any filesystem level snapshotting (like with ZFS),
>> splitting the filespaces will make it harder to do restores and using
>> snapshots.
>>
>> On Mon, Apr 6, 2020 at 10:40 AM Ed Behn <ed(dot)behn(at)collins(dot)com> wrote:
>>
>>> I was once told that it's best practice to store tables and indexes in
>>> separate tablespaces located on separate physical drives. It seemed logical
>>> that this should improve performance because the read-head wouldn't need to
>>> jump back and forth between a table and its index.
>>>
>>> However, I can't seem to find this advice anywhere online. Is it indeed
>>> best practice? Is it worth the hassle?
>>>
>>>
>>>
>>
>> As a general and practical matter I 100% agree with Erik -- the advice is
> a bit out of date, and for SSDs it probably makes no meaningful difference.
> However for extremely high, sustained workloads, you might find splitting
> tables, indices, and transaction logs onto separate disk _disk arrays and
> controllers_ could yield improvements, particularly for certain RAID
> setups. But maxing out a disk controller is pretty hard to do (impossible
> afaik with a single drive), so you'd want to have some strong metrics to
> show this is worth it. At that point, you'd probably be better off getting
> commercial disk array solutions into the mix rather than rolling your own
> anyway..
>
> Steve
>
>
>