Low cache hit ratio

Hello,

I have recently deployed a new Slave (streaming replication) and have been monitoring its cache hit ratio.

At the moment, read-only queries are being sent to this slave but only 10% of the traffic.
The cache hit ratio is now at 82%. This database is around 1.4TB and is running on EC2 instances in AWS. PostgreSQL version is 9.2.24.

The instance is a r4.2xlarge, so it's got 8 vCPUs and 61GB of RAM. The postgresql.conf file can be seen below (will show only relevant parameters for the cache/performance):

> hot_standby = on
> random_page_cost = 1.1
> max_connections = 500
> shared_buffers = 15GB
> statement_timeout = 0
> work_mem = 31457kB
> maintenance_work_mem = 2GB
> wal_level = hot_standby
> fsync = on
> synchronous_commit = on
> wal_buffers = 16MB
> checkpoint_segments = 32
> checkpoint_completion_target = 0.9
> max_wal_senders = 20
> wal_keep_segments = 1024
> effective_cache_size = 45GB
> logging_collector = on
> autovacuum = on
> log_autovacuum_min_duration = 1000
> autovacuum_max_workers = 5
> autovacuum_naptime = 40s
> autovacuum_vacuum_threshold = 200
> autovacuum_analyze_threshold = 150
> autovacuum_vacuum_scale_factor = 0.02
> autovacuum_analyze_scale_factor = 0.005
> deadlock_timeout = 2s
> max_files_per_process = 4096
> effective_io_concurrency = 200
> hot_standby_feedback = on
> max_standby_streaming_delay = 120s
> default_statistics_target = 100

I have tried reducing the shared_buffers parameter from 15GB to 8GB, but the cache hit ratio went down to 60%.

Do you guys have any suggestions, on what I could try to get this cache more hits?

Thanks in advance!

---
Regards,

Lucas

> This message is encrypted. Both the Public Key and the GPG encrypted message are included in this email so that you can verify its origin.