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Re: Reliability with RAID 10 SSD and Streaming Replication - Mailing list pgsql-performance

From Cuong Hoang
Subject Re: Reliability with RAID 10 SSD and Streaming Replication
Date
Msg-id CAAE-9WFQA6B2X6XJV6m+bir6jq2WA-RQLkzUA0GCrMFprMMgOw@mail.gmail.com
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In response to Re: Reliability with RAID 10 SSD and Streaming Replication  (Tomas Vondra <tv@fuzzy.cz>)
Responses Re: Reliability with RAID 10 SSD and Streaming Replication  (Tomas Vondra <tv@fuzzy.cz>)
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Hi Tomas,

We have a lot of small updates and some inserts. The database size is at 35GB including indexes and TOAST. We think it will keep growing to about 200GB. We usually have a burst of about 500k writes in about 5-10 minutes which basically cripples IO on the current servers. I've tried to increase the checkpoint_segments, checkpoint_timeout etc. as recommended in "PostgreSQL 9.0 Performance" book. However, it seems like our server just couldn't handle the current load.

Here is the server specs:

Dual E5620, 32GB RAM, 4x1TB SAS 15k in RAID10

Here are some core PostgreSQL configs:

shared_buffers = 2GB                    # min 128kB
work_mem = 64MB                         # min 64kB
maintenance_work_mem = 1GB              # min 1MB
wal_buffers = 16MB
checkpoint_segments = 128
checkpoint_timeout = 30min
checkpoint_completion_target = 0.7


Thanks,
Cuong


On Fri, May 17, 2013 at 10:06 AM, Tomas Vondra <tv@fuzzy.cz> wrote:
Hi,

On 16.5.2013 16:46, Cuong Hoang wrote:
> Hi all,
>
> Our application is heavy write and IO utilisation has been the problem
> for us for a while. We've decided to use RAID 10 of 4x500GB Samsung 840

What does "heavy write" mean in your case? Does that mean a lot of small
transactions or few large ones?

What have you done to tune the server?

> Pro for the master server. I'm aware of write cache issue on SSDs in
> case of power loss. However, our hosting provider doesn't offer any
> other choices of SSD drives with supercapacitor. To minimise risk, we
> will also set up another RAID 10 SAS in streaming replication mode. For
> our application, a few seconds of data loss is acceptable.

Streaming replication allows zero data loss if used in synchronous mode.

> My question is, would corrupted data files on the primary server affect
> the streaming standby? In other word, is this setup acceptable in terms
> of minimising deficiency of SSDs?

It should be.

Have you considered using a UPS? That would make the SSDs about as
reliable as SATA/SAS drives - the UPS may fail, but so may a BBU unit on
the SAS controller.

Tomas


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