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> On Mar 10, 2021, at 15:03, Ron <ronljohnso...@gmail.com> wrote: > On 3/10/21 11:56 AM, Martín Fernández wrote: >> >> >>> On 10 Mar 2021, at 11:25, Ron <ronljohnso...@gmail.com> wrote: >>> >>>> On 3/10/21 2:10 AM, Radoslav Nedyalkov wrote: >>>> >>>> On Wed, Mar 10, 2021 at 3:56 AM Martín Fernández <fmarti...@gmail.com> >>>> wrote: >>>>> Hello, >>>>> >>>>> I’m troubleshooting a problem at my company with a pg 12 cluster that we >>>>> run. >>>>> >>>>> We are using Amazon DMS to replicate data from our database into S3 >>>>> buckets. DMS replicates data by using logical replication slots. >>>>> >>>>> After introducing DMS in our environment, we have seen an increase in CPU >>>>> load of 20 points at business hours (from ~60% to ~80%). >>>>> >>>>> The other thing that we have identified is that AccessShareLocks increase >>>>> considerably when DMS running. >>>>> >>>>> Based on this information, I’m trying to understand if this is something >>>>> expected when running logical replication or not. We’ve been running >>>>> physical replication for several years and we haven’t seen nothing like >>>>> this. It could be the case that the issue is not related at all with >>>>> logical replication and is purely a DMS artifact. >>>>> >>>>> Thanks before hand! >>>>> >>>>> Best, >>>>> Martín >>>> >>>> Hi, >>>> >>>> I would check in pg_stat_activity what those logical replication slots do. >>>> I guess COPY. >>> >>> If it's a full-load or full-load-and-cdc, then it's almost certainly a COPY. >> >> We are doing full-load and full-load-and-cdc. At this point it’s just cdc >> since the full load was done month ago. > > Then it's "just" logical replication. Right! > >>> >>>> Are you doing one shot copy ? every day ? Then copying all the tables will >>>> lead to load increase. >>>> How many tables at a time DMS copies? It should be configurable. >>> >>> It definitely is, with the MaxFullLoadSubTasks parameter. The default is 8. >> >> We are copying a lot of tables. 100+ > > If right now you're just doing CDC replication, then you're synchronizing > lots of tables. How often are they modified? > Yes, used the word copying incorrectly. Last time we paused DMS we acumulated 180GB in the replication slot in 1 hour. >>> >>>> AccessShareLock is absolutely normal. You have a transaction doing SELECT >>>> (COPY) over a table. >>> >>> If DMS with Postgresql as the source is anything like when Oracle is the >>> source (we're testing Oracle -> RDS Postgresql) then it starts a >>> SERIALIZABLE transaction. >> >> My guess at this point is that the CPU load increases due to the increase of >> AccessShareLocks, is that a fair assumption ? Have you seen a similar >> behavior in Oracle ? > > I don't have access to the Oracle database, and so far we're just testing on > the low-volume QA system. > > Further, I don't know enough about how logical replication works to have an > opinion. > > -- > Angular momentum makes the world go 'round.
