postgresql: WIP script to recollate the database

hosts/by-name/servo/services/postgresql/recollate.sh

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+#!/bin/sh
+# source: <https://gist.githubusercontent.com/troykelly/616df024050dd50744dde4a9579e152e/raw/fe84e53cedf0caa6903604894454629a15867439/reindex_and_refresh_collation.sh>
+#
+# run this whenever postgres complains like:
+# > WARNING:  database "gitea" has a collation version mismatch
+# > DETAIL:  The database was created using collation version 2.39, but the operating system provides version 2.40.
+# > HINT:  Rebuild all objects in this database that use the default collation and run ALTER DATABASE gitea REFRESH COLLATION VERSION, or build PostgreSQL with the right library version.
+#
+# this script checks which databases are in need of a collation update,
+# and re-collates them as appropriate.
+# invoking this script should have low perf impact in the non-upgrade case,
+# so safe to do this as a cron job.
+#
+# invoke as postgres user
+
+log_info() {
+  >&2 echo "$@"
+}
+
+list_databases() {
+  log_info "Retrieving list of databases from the PostgreSQL server..."
+  psql --dbname="postgres" -Atc \
+    "SELECT datname FROM pg_database WHERE datistemplate = false"
+}
+
+refresh_collation_version() {
+  local db=$1
+  log_info "Refreshing collation version for database: $db..."
+  psql --dbname="$db" -c \
+    "ALTER DATABASE \"$db\" REFRESH COLLATION VERSION;"
+}
+
+check_collation_mismatches() {
+  local error=
+  log_info "Checking for collation mismatches in all databases..."
+  # Loop through each database and check for mismatching collations in table columns.
+  while IFS= read -r db; do
+    if [ -n "$db" ]; then
+      log_info "Checking database: $db for collation mismatches..."
+      local mismatches=$(psql --dbname="$db" -Atc \
+        "SELECT 'Mismatch in table ' || table_name || ' column ' || column_name || ' with collation ' || collation_name
+         FROM information_schema.columns
+         WHERE collation_name IS NOT NULL AND collation_name <> 'default' AND table_schema = 'public'
+         EXCEPT
+         SELECT 'No mismatch - default collation of ' || datcollate || ' used.'
+         FROM pg_database WHERE datname = '$db';"
+      )
+      if [ -z "$mismatches" ]; then
+        log_info "No collation mismatches found in database: $db"
+      else
+        # Print an informational message to stderr.
+        log_info "Collation mismatches found in database: $db:"
+        log_info "$mismatches"
+        error=1
+      fi
+    fi
+  done
+
+  if [ -n "$error" ]; then
+    exit 1
+  fi
+}
+
+log_info "Starting the reindexing and collation refresh process for all databases..."
+
+databases=$(list_databases)
+
+if [ -z "$databases" ]; then
+  log_info "No databases found for reindexing or collation refresh. Please check connection details to PostgreSQL server."
+  exit 1
+fi
+
+for db in $databases; do
+  refresh_collation_version "$db"
+done
+
+# Checking for collation mismatches after reindexing and collation refresh.
+# Pass the list of databases to the check_collation_mismatches function through stdin.
+echo "$databases" | check_collation_mismatches
+
+log_info "Reindexing and collation refresh process completed."