Setting sysctl values v23.44.0

By default, TPA sets various sysctl values on target instances, and includes them in /etc/sysctl.conf so that they persist across reboots.

You can optionally specify your own values in sysctl_values:

cluster_vars:
  sysctl_values:
    kernel.core_pattern: core.%e.%p.%t
    vm.dirty_bytes: 4294967296
    vm.zone_reclaim_mode: 0

Any values you specify will take precedence over TPA's default values for that variable (if any). The settings will first be added to sysctl.conf line-by-line, and finally loaded with sysctl -p.

Docker and lxd instances do not support setting sysctls, so TPA will skip this step altogether for those platforms.

Hugepages

By default, TPA reserves hugepages of the architecture's default size (2MB on x86_64) for Postgres to use for shared_buffers. It does this by adding hugepages=N to the kernel command line and writing vm.nr_hugepages = N to /etc/sysctl.conf.

If you want Postgres to use a larger hugepage size (typically 1GB on x86_64), set huge_page_size to a Postgres-style memory string:

instances:
- Name: primary
  vars:
    huge_page_size: 1GB

When huge_page_size is set, TPA will:

• reserve pages of that size on the kernel command line, e.g. hugepagesz=1G hugepages=N;
• omit vm.nr_hugepages from /etc/sysctl.conf (that sysctl only ever applies to the architecture's default-size pool, and is silently ineffective for any other size); and
• set the huge_page_size GUC in postgresql.conf so Postgres uses pages from the chosen pool.

It is almost always right to set huge_page_size on individual Postgres instances rather than in cluster_vars: any reservation made on the kernel command line is taken out of normal memory at boot, so a Barman server or other non-Postgres instance in the same cluster does not want the same allocation as a Postgres node.

By default, TPA calculates the number of hugepages to reserve as shared_buffers plus 3% of total RAM, divided by the hugepage size. You can override this calculation by setting nr_hugepages directly:

instances:
- Name: primary
  vars:
    huge_page_size: 1GB
    nr_hugepages: 16

Transparent hugepages

By default, TPA will set transparent_hugepage to "never" on the kernel command line and also install a script, /etc/tpa/rc.local, to set it at boot-time via the sys filesystem. To use a different setting, set transparent_hugepage to always or madvise in an instances vars or in cluster_vars to control all instances.