perf(grafana-db): raise archive_timeout to 30min on gf-pg

A WAL segment is a fixed 16 MiB file. archive_timeout forces a segment
switch on a timer so the archive never trails reality by more than that
interval, and the switched-out segment is written and archived at its full
16 MiB no matter how few bytes of real WAL it holds. CNPG defaults this to
5min, which permits up to 288 segments/day = 4.6 GB/day per cluster.

Measured on gf-pg: the database is 21 MB and generates 4.5 MB/day of actual
WAL, while its RBD volume takes 211 MB/hour -- against 192 MB/hour predicted
from 12 switches of 16 MiB. Essentially every byte written to this volume is
padding, roughly 1100x amplification.

This resolves an anomaly that has been open since the start of the endurance
work: gf-pg appeared to write gigabytes per day for a 21 MB database, and
neither WAL volume nor data changes could account for it. Segment padding
does, exactly.

Applied to gf-pg alone as a staged rollout. It is the lowest-risk cluster
and gives the cleanest signal -- its real WAL is small enough that any change
in volume is unambiguously attributable to this parameter. The same default
affects all seven clusters and is worth an estimated ~24 GB/day of logical
writes fleet-wide, but that only goes ahead once this one is verified.

The cost is RPO. On total loss of the cluster, up to 30min of Grafana state
becomes unrecoverable instead of 5min. That state is dashboards, annotations
and preferences, changing at ~4.5 MB/day, so the window is nearly always
empty. Clusters holding credentials or job state get evaluated separately
rather than inheriting this value by default.

archive_timeout is in CNPG's GlobalDefaultSettings, not its
FixedConfigurationParameters, so it is user-overridable -- verified against
pkg/postgres/configuration.go rather than assumed.

Context: drive-endurance work on three QLC NVMe OSDs at 81-87% wear.

kubernetes/apps/authentik/cluster.yaml

@@ -63,7 +63,10 @@ spec:
       # on an unclean shutdown is not an acceptable trade.
       checkpoint_timeout: "15min"
       max_wal_size: "2GB"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
     # Async replication makes CNPG switchover slow because the standby has
     # to chase missing WAL via barman-cloud and replay queued records
     # before it can promote. With one synchronous standby, the standby is

kubernetes/apps/grafana-db/postgres.yaml

@@ -49,7 +49,32 @@ spec:
       # on an unclean shutdown is not an acceptable trade.
       checkpoint_timeout: "15min"
       max_wal_size: "2GB"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
+      # THE dominant write source on this cluster, by three orders of magnitude.
+      #
+      # A WAL segment is a fixed 16 MiB file. archive_timeout forces a segment
+      # switch on a timer so the archive never lags reality by more than that
+      # interval -- and the switched-out segment is written and archived at its
+      # full 16 MiB regardless of how few bytes of real WAL it contains.
+      #
+      # CNPG defaults this to 5min, i.e. up to 288 segments/day = 4.6 GB/day.
+      # Measured here: this database is 21 MB and generates 4.5 MB/day of actual
+      # WAL, while its RBD volume takes 211 MB/hour. Essentially every byte
+      # written is padding -- roughly 1100x amplification.
+      #
+      # 30min cuts that to 48 segments/day. The cost is RPO: on total loss of
+      # the cluster, up to 30min of Grafana state is unrecoverable rather than
+      # 5min. Grafana's state here is dashboards, annotations and preferences,
+      # and the write rate says it changes ~4.5 MB/day -- so that window is
+      # nearly always empty anyway.
+      #
+      # Applied to gf-pg FIRST, alone, as a staged rollout: it is the lowest-risk
+      # cluster and has the cleanest signal, since its real WAL is small enough
+      # that any change in volume is unambiguously this parameter.
+      archive_timeout: "30min"
   resources:
     requests:
       cpu: 100m

kubernetes/apps/home-assistant/ha-pg-cluster.yaml

@@ -85,12 +85,26 @@ spec:
       # Compress full-page images in WAL. Recorder writes are many small row
       # inserts scattered across pages, so full-page writes after each
       # checkpoint dominate WAL volume; compression cuts that directly.
-      wal_compression: "on"
+      #
+      # Measured on this cluster: full-page images are 62.4% of WAL bytes, so
+      # this is the single largest lever on recorder write volume.
+      #
+      # zstd, not "on": the boolean spelling resolves to pglz, the original
+      # 2016-era algorithm, which is both slower and weaker than the two
+      # alternatives PostgreSQL 16 accepts here (lz4, zstd). zstd gives the
+      # best ratio on 8 KiB page images, and the CPU cost lands on a cluster
+      # that is IO-bound on QLC NVMe, not CPU-bound.
+      wal_compression: "zstd"
       # Fewer checkpoints => fewer full-page writes, since a page is only
-      # fully-logged on its first modification after a checkpoint. 15min with a
-      # 2GB ceiling keeps recovery time sane while cutting repeat full-page
-      # images for the hot rows the recorder rewrites constantly.
-      checkpoint_timeout: "15min"
+      # fully-logged on its first modification after a checkpoint. Doubling the
+      # interval halves how often each hot page pays that 8 KiB toll.
+      #
+      # Recovery cost is bounded by how much WAL a single interval produces,
+      # not by the interval itself: at the measured rate 30min is well under
+      # 200MB of replay, i.e. seconds. max_wal_size stays 2GB precisely so the
+      # timeout stays the binding trigger -- if size were the binding one, the
+      # interval change would do nothing.
+      checkpoint_timeout: "30min"
       max_wal_size: "2GB"
       min_wal_size: "512MB"
       # full_page_writes is deliberately LEFT ON (the default). RBD can tear a

kubernetes/apps/immich/cluster.yaml

@@ -42,7 +42,10 @@ spec:
     parameters:
       shared_buffers: "512MB"
       max_wal_size: "2GB"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
       # Write-reduction tuning. These databases are largely idle, and the
       # Postgres defaults favour throughput over storage that wears out.
       #

kubernetes/apps/paperless/cluster.yaml

@@ -54,7 +54,10 @@ spec:
       # on an unclean shutdown is not an acceptable trade.
       checkpoint_timeout: "15min"
       max_wal_size: "2GB"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
     # See ak-pg cluster.yaml for the rationale on synchronous replication.
     synchronous:
       method: any

kubernetes/apps/trmnl/cluster.yaml

@@ -32,7 +32,10 @@ spec:
     parameters:
       shared_buffers: "128MB"
       max_connections: "50"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
       # Write-reduction tuning. These databases are largely idle, and the
       # Postgres defaults favour throughput over storage that wears out.
       #

kubernetes/apps/woodpecker/cluster.yaml

@@ -76,7 +76,10 @@ spec:
       # on an unclean shutdown is not an acceptable trade.
       checkpoint_timeout: "15min"
       max_wal_size: "2GB"
-      wal_compression: "on"
+      # zstd, not "on": the boolean spelling resolves to pglz (2016-era, weaker
+      # and slower than the lz4/zstd this build also accepts). Compresses the
+      # full-page images that dominate WAL volume after each checkpoint.
+      wal_compression: "zstd"
   resources:
     requests:
       cpu: 100m