Re: Another streaming replication question

[Mark Steben <mark.steben@xxxxxxxxxxxxxxxxx>]

Thank you Rui for your feedback.  It will be very valuable in my ultimate solution I'm sure. 

On Tue, Nov 6, 2018 at 4:09 PM Rui DeSousa <rui@xxxxxxxxxxxxx> wrote:

On Nov 6, 2018, at 12:13 PM, Mark Steben <mark.steben@xxxxxxxxxxxxxxxxx> wrote:

   1.  Can streaming replication work in this high-load situation?

Yes, given you have low latency and the bandwidth to support it.  

Need to plan for cases when streaming does fall behind too; don’t want streaming to just break.

Some options:

1. Replication slot on the upstream sever

2. Allow streaming to fallback to restoring WALs from archive

3. Both of the above options

   2.  What, if anything, can I do to make it work better?  Perhaps convert to cascade? Master -->standby1 ---> standby2

That would help in managing you bandwidth between nodes.

There is a lot to consider and it really depends on your use cases and your application/queries.

A few rhetorical questions: 

What is the replicas being used for?  

What an acceptable replication lag?

What an acceptable apply lag?

Should queries be killed to apply replica transactions?

What’s your vacuum strategy as that impacts replicas?

These two parameters I find invaluable (their validity depends on your use case). 

hot_standby_feedback = true

max_standby_streaming_delay = 30s

The other big thing is query performance and I/O as each has a large impact on replication lag.  So plan for tuning.

--

Mark Steben
 Database Administrator
@utoRevenue | Autobase 
  CRM division of Dominion Dealer Solutions 
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