Re: Logical replication very slow

[Achilleas Mantzios]

On 25/2/19 2:06 μ.μ., Boris Sagadin wrote:

I think it should. I set it to unlogged on target/slave server only. One other 
table which is much smaller and already replicated receives changes from master.

Ah, ok then.

About settings copy_data to false, nice idea, I'll try that too and compare 
speed.

Please note that ppl here tend to not encourage top posting. Generally It's ok 
for business emails elsewhere, but here straight quoting is better and more 
accurate.

On Mon, Feb 25, 2019 at 9:51 AM Achilleas Mantzios <ach...@matrix.gatewaynet.com 
<mailto:ach...@matrix.gatewaynet.com>> wrote:

    On 25/2/19 9:59 π.μ., Boris Sagadin wrote:

    Doing an initial replica.

    postgres 119454 93.5 25.9 34613692 32649656 ?   Rs   07:16  32:45  \_ 
postgres: 10/main: bgworker: logical replication worker for subscription 24783 
sync 16500

    I've cancelled the sync, set the tables to unlogged type and started it 
again. I think it helped, still much slower than binary, but better, about 
40MB/s. Will set them back to logged type
    after initial replica is done.

    Will this work at all? Doesn't unlogged mean no changes are written to the 
WAL? What if you just copy by dump and then just add and refresh without 
|copy_data ?
    |

    After the initial replica, there aren't that many updates, so it's OK then. 
But if a need for a new slave arises, waiting a few days for initial replica to 
finish, which in binary replication
    case is just hours, can be a big problem for us.

    Boris



    On Mon, Feb 25, 2019 at 8:08 AM Achilleas Mantzios <ach...@matrix.gatewaynet.com 
<mailto:ach...@matrix.gatewaynet.com>> wrote:

        On 25/2/19 8:52 π.μ., Boris Sagadin wrote:

        Doing an initial replica and trying to find a bottleneck, Ubuntu 16.04, 
NVMe disks, PgSQL v10.7, AWS. With binary replication, DB is replicated at good 
speed, around 500MB/s. Trying LR now
        for a big table (about 1.4TB with 2 indexes) and the speed is only 
about 2MB/s.

        Is logical replication subscriber in "streaming" state or in initial 
snapshot? What's the behavior after the initial snapshot, when it gets into streaming 
state?

        Checked disk util with iostat and only about 20% utilized on master, 15% on 
target, CPU load on master is low. On slave I can see the "logical replication 
worker" process is taking about
        70% CPU time on a single core, machine has 16 cores.

        Is there a setting I am missing here? Any ideas appreciated.

        Boris

-- Achilleas Mantzios

        IT DEV Lead
        IT DEPT
        Dynacom Tankers Mgmt

-- Achilleas Mantzios

    IT DEV Lead
    IT DEPT
    Dynacom Tankers Mgmt

--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt