Segment fadvise

[kjnilsson]

Make segment fadvise option configurable.

It is not clear if random or normal is the better option for external read plan segment reads so this is now configurable.

This setting also affects segments opened for append as when the segment is full and is closed we perform an fadvise call. By default this is set to dont_need to ensure page cache data is reclaimed after a segment flush.

When closing the WAL we also set dont_need advise as this data is unlikely to ever be read again.

[the-mikedavis]

I tested this locally on rabbitmq/rabbitmq-server#12713 with:

perf-test -qq -u qq -x 1 -y 0 -c 1000 -s 4000 -ms -C 5000000

before (7406ed2):

$ free -wh
               total        used        free      shared     buffers       cache   available
Mem:           125Gi        10Gi        54Gi       1.2Gi       3.2Gi        60Gi       115Gi

after (ddfbec9):

$ free -wh
               total        used        free      shared     buffers       cache   available
Mem:           125Gi       9.9Gi        74Gi       1.2Gi       3.2Gi        40Gi       115Gi

🚀

[kjnilsson]

I tested this locally on rabbitmq/rabbitmq-server#12713 with:

perf-test -qq -u qq -x 1 -y 0 -c 1000 -s 4000 -ms -C 5000000

before (7406ed2):

$ free -wh
               total        used        free      shared     buffers       cache   available
Mem:           125Gi        10Gi        54Gi       1.2Gi       3.2Gi        60Gi       115Gi

after (ddfbec9):

$ free -wh
               total        used        free      shared     buffers       cache   available
Mem:           125Gi       9.9Gi        74Gi       1.2Gi       3.2Gi        40Gi       115Gi

🚀

thanks! what kind of machine do you have with 126Gi RAM?

[the-mikedavis]

It's a custom-built desktop, I went a little overboard on the memory 😅