Re: [HACKERS] [PATCH] guc-ify the formerly hard-coded MAX_SEND_SIZEto max_wal_send - Mailing list pgsql-hackers

From Andres Freund
Subject Re: [HACKERS] [PATCH] guc-ify the formerly hard-coded MAX_SEND_SIZEto max_wal_send
Date
Msg-id 20170105190119.oe4gtbknbv2637fv@alap3.anarazel.de
Whole thread Raw
In response to [HACKERS] [PATCH] guc-ify the formerly hard-coded MAX_SEND_SIZE to max_wal_send  (Jonathon Nelson <jdnelson@dyn.com>)
List pgsql-hackers
Hi,

On 2017-01-05 12:55:44 -0600, Jonathon Nelson wrote:
> Attached please find a patch for PostgreSQL 9.4 which changes the maximum
> amount of data that the wal sender will send at any point in time from the
> hard-coded value of 128KiB to a user-controllable value up to 16MiB. It has
> been primarily tested under 9.4 but there has been some testing with 9.5.
> 
> In our lab environment and with a 16MiB setting, we saw substantially
> better network utilization (almost 2x!), primarily over high bandwidth
> delay product links.

That's a bit odd - shouldn't the OS network stack take care of this in
both cases?  I mean either is too big for TCP packets (including jumbo
frames).  What type of OS and network is involved here?

Greetings,

Andres Freund



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