> 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 >> <mailto: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. > >> 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+ > >> 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 ? > >> Physical replication is a different thing. It happens at another level. >> >> Regards >> Rado > > -- > Angular momentum makes the world go 'round.
