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

@@ -67,20 +67,6 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 3.2 GB/day here, most of it padding.
-      #
-      # 15min, NOT the 30min used elsewhere in this rollout. This cluster holds
-      # credentials, sessions and enrolment state, so its RPO is worth more than
-      # the difference: 30min would save a further 0.3 GB/day, which does not
-      # justify doubling the worst-case loss window on this data.
-      #
-      # It does carry a synchronous standby (instances: 2), so the realistic
-      # exposure is losing both instances, not one -- but the conservative value
-      # is cheap here and the aggressive one buys almost nothing.
-      archive_timeout: "15min"
     # 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/home-assistant/ha-pg-cluster.yaml

@@ -86,26 +86,8 @@ spec:
       # inserts scattered across pages, so full-page writes after each
       # checkpoint dominate WAL volume; compression cuts that directly.
       #
-      # Full-page images really are ~62% of WAL here: 61.9% measured as a
-      # steady-state delta over one checkpoint cycle, against 62.4% lifetime.
-      #
-      # But switching pglz -> zstd changed NOTHING. Measured by
-      # pg_current_wal_lsn advance over 20min windows: 4911 and 4976 MB/day
-      # before, 5002 MB/day after.
-      #
-      # The reason is that `wal_compression: "on"` was never "no compression" --
-      # it is pglz, which was already compressing these page images. zstd only
-      # changes the ratio, and on recorder pages that margin is too small to
-      # measure. The original framing of this change (that the clusters "were
-      # not getting compression") was wrong; they were.
-      #
-      # Note the 62% figure is an upper bound: it is computed as
-      # wal_fpi * 8192 / wal_bytes, which assumes uncompressed 8 KiB pages. With
-      # compression active the true byte share is lower, which is consistent
-      # with there being little headroom left for a better algorithm.
-      #
-      # Kept because zstd is not worse than pglz and costs nothing. It is simply
-      # not a lever. The real one on this cluster was archive_timeout, below.
+      # 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
@@ -113,35 +95,9 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 4.6 GB/day that is largely padding.
-      #
-      # Verified on gf-pg first (the staged rollout): 211 -> 41 MB/hour, an 81%
-      # cut, with archived segments falling from ~12/hour to ~1.5/hour in step.
-      # Two independent signals moving together is what confirms the volume was
-      # padding rather than data.
-      #
-      # The cost is RPO: up to 30min of WAL is unrecoverable if this cluster and
-      # its volume are lost outright. This is a single-instance cluster, so the
-      # archive is the only off-node copy.
-      archive_timeout: "30min"
       # Fewer checkpoints => fewer full-page writes, since a page is only
-      # fully-logged on its first modification after a checkpoint.
-      #
-      # That reasoning did not show up in WAL volume: 15min -> 30min moved the
-      # WAL rate not at all (4911/4976 -> 5002 MB/day). The likely reason is
-      # that this workload is append-mostly -- a page is dirtied while it fills
-      # and then not touched again, so its full-page image is paid once
-      # regardless of how often checkpoints run. Interval only helps pages that
-      # are re-dirtied across many cycles, which is not what a recorder does.
-      #
-      # Kept, but NOT because WAL improved. checkpoint_timeout also governs
-      # data-file writes at checkpoint, and those are unmeasured here: this
-      # volume takes ~11 GB/day against 4.9 GB/day of WAL, so most of its
-      # traffic is outside what the WAL measurement covers. Revisit with a
-      # data-file measurement before treating this value as justified.
+      # 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

kubernetes/apps/immich/cluster.yaml

@@ -46,20 +46,6 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 4.6 GB/day that is largely padding.
-      #
-      # Verified on gf-pg first (the staged rollout): 211 -> 41 MB/hour, an 81%
-      # cut, with archived segments falling from ~12/hour to ~1.5/hour in step.
-      # Two independent signals moving together is what confirms the volume was
-      # padding rather than data.
-      #
-      # The cost is RPO: up to 30min of WAL is unrecoverable if this cluster and
-      # its volume are lost outright. This is a single-instance cluster, so the
-      # archive is the only off-node copy.
-      archive_timeout: "30min"
       # Write-reduction tuning. These databases are largely idle, and the
       # Postgres defaults favour throughput over storage that wears out.
       #

kubernetes/apps/paperless/cluster.yaml

@@ -58,18 +58,6 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 4.1 GB/day that is largely padding.
-      #
-      # Verified on gf-pg first (the staged rollout): 211 -> 41 MB/hour, an 81%
-      # cut, with archived segments falling from ~12/hour to ~1.5/hour in step.
-      #
-      # The cost is RPO: up to 30min of WAL is unrecoverable if both instances
-      # are lost. The documents themselves live on the media PVC, not in
-      # Postgres -- this database holds their metadata.
-      archive_timeout: "30min"
     # See ak-pg cluster.yaml for the rationale on synchronous replication.
     synchronous:
       method: any

kubernetes/apps/trmnl/cluster.yaml

@@ -36,20 +36,6 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 4.6 GB/day that is largely padding.
-      #
-      # Verified on gf-pg first (the staged rollout): 211 -> 41 MB/hour, an 81%
-      # cut, with archived segments falling from ~12/hour to ~1.5/hour in step.
-      # Two independent signals moving together is what confirms the volume was
-      # padding rather than data.
-      #
-      # The cost is RPO: up to 30min of WAL is unrecoverable if this cluster and
-      # its volume are lost outright. This is a single-instance cluster, so the
-      # archive is the only off-node copy.
-      archive_timeout: "30min"
       # Write-reduction tuning. These databases are largely idle, and the
       # Postgres defaults favour throughput over storage that wears out.
       #

kubernetes/apps/woodpecker/cluster.yaml

@@ -80,20 +80,6 @@ spec:
       # 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"
-      # A WAL segment is a fixed 16 MiB file, and archive_timeout forces a switch
-      # on a timer -- the segment is then written and archived at its full size
-      # no matter how little real WAL it holds. CNPG defaults to 5min, i.e. up
-      # to 288 segments/day = 4.6 GB/day that is largely padding.
-      #
-      # Verified on gf-pg first (the staged rollout): 211 -> 41 MB/hour, an 81%
-      # cut, with archived segments falling from ~12/hour to ~1.5/hour in step.
-      # Two independent signals moving together is what confirms the volume was
-      # padding rather than data.
-      #
-      # The cost is RPO: up to 30min of WAL is unrecoverable if this cluster and
-      # its volume are lost outright. This is a single-instance cluster, so the
-      # archive is the only off-node copy.
-      archive_timeout: "30min"
   resources:
     requests:
       cpu: 100m