Re: How to speed WAL apply in destination

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On 12/9/22 05:57, SASIKUMAR Devaraj wrote:
During certain interval there is huge WAL file generation f3om primary around 300gb/hr which delays sync in secondary by atleast 30 mins. Other time it is normal 

On Fri, Dec 9, 2022 at 4:20 PM, Laurenz Albe
<laurenz.albe@xxxxxxxxxxx> wrote:
On Fri, 2022-12-09 at 08:47 +0000, Bryon Roché wrote:

> On December 9, 2022 5:02:59 AM UTC, SASIKUMAR Devaraj <sashikumard@xxxxxxxxx> wrote:
> > How to speed up WAL apply process in secondary? Any parameter available from postgres, apart from disk speed? 
> There are fsync parameters which can be set to off that may provide a modest speed increase, at the cost of removing crash safety.

That is spectacularly bad advice.

Is the disk the bottleneck at all?

Laurenz Albe

You can use "ionice" and "chrt" to make WAL writer and WAL sender real time I/O priority.  Also, you should consider increasing the network throughput between the primary and the secondary. What kind of network is there? Is any of the servers a virtual machine? Most of the hypervisors throttle network adapters of the virtual machines. Default network speed for VMWare VMs is 1Gb/sec. I think that the same is true for KVM. You should check the disk bandwidth consumption by using sar -d or atop -d. The first step would be to use iperf3 to check the network throughput.

Mladen Gogala
Database Consultant
Tel: (347) 321-1217

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