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postgresql: drop per-database autovacuum ALTERs (rejected by Postgres)

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Follow-up to the previous two commits: the ALTER DATABASE ... SET
autovacuum_* commands fail at boot with

  ERROR: parameter "autovacuum_vacuum_scale_factor" cannot be changed now

and take matrix-synapse-db-tune.service (and nextcloud-db-init.service)
down with them.

Root cause: ALTER DATABASE/ROLE ... SET validates through
set_config_option() with an interactive context, and guc.c rejects any
PGC_SIGHUP parameter set that way. All autovacuum_* GUCs are
SIGHUP-context, so per-database scoping is impossible for them — only
USERSET-level parameters (e.g. work_mem, statement_timeout) can be set
per-database.

Nothing is lost: the same values are already set cluster-wide in
configuration.nix, which covers both nextclouddb and matrix-synapse.
Remove the ALTERs from nextcloud-db-init and delete the now-purposeless
matrix-synapse-db-tune service.
This commit is contained in:
Sovran Contributor
2026-09-21 14:21:01 -05:00
committed by naturallaw777
parent e31094c194
commit 8bc325b148
2 changed files with 5 additions and 34 deletions
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modules/synapse.nix
-29
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@@ -60,35 +60,6 @@ lib.mkIf config.sovran_systemsOS.services.synapse {
'';
};
# ── Per-database Postgres tuning (matrix-synapse only) ─────
# Mirrors the nextclouddb tuning: Synapse's state and event tables are
# write-heavy and bloat fast under stock autovacuum. Scoped via ALTER
# DATABASE so each DB gets what suits it. Idempotent.
systemd.services.matrix-synapse-db-tune = {
description = "Apply per-database Postgres tuning for Matrix Synapse";
after = [ "postgresql.service" ];
requires = [ "postgresql.service" ];
before = [ "matrix-synapse.service" ];
wantedBy = [ "multi-user.target" ];
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
};
path = [ config.services.postgresql.package pkgs.coreutils ];
script = ''
set -euo pipefail
# Wait for ensureDatabases to have created the DB on first boot.
for i in $(seq 1 30); do
if psql -U postgres -lqt | cut -d \| -f 1 | grep -qw "matrix-synapse"; then
break
fi
sleep 2
done
psql -U postgres -d matrix-synapse -c "ALTER DATABASE \"matrix-synapse\" SET autovacuum_vacuum_scale_factor = '0.05';"
psql -U postgres -d matrix-synapse -c "ALTER DATABASE \"matrix-synapse\" SET autovacuum_analyze_scale_factor = '0.025';"
'';
};
# ── Generate runtime config from domain files ───────────────
systemd.services.matrix-synapse-runtime-config = {
description = "Generate Synapse runtime config from domain files";