auto tune based on memory

lib/charms/postgresql_k8s/v0/postgresql.py

@@ -428,11 +428,21 @@ def build_postgresql_parameters(
 
         Args:
             profile: the profile to use.
-            available_memory: available memory to use in calculation
+            available_memory: available memory to use in calculation in bytes.
 
         Returns:
             Dictionary with the PostgreSQL parameters.
         """
         logger.debug(f"Building PostgreSQL parameters for {profile=} and {available_memory=}")
         if profile == "production":
-            return {"shared_buffers": "987MB", "effective_cache_size": "2958MB"}
+            # Use 25% of the available memory for shared_buffers.
+            # and the remaind as cache memory.
+            shared_buffers = int(available_memory * 0.25)
+            effective_cache_size = int(available_memory - shared_buffers)
+
+            parameters = {
+                "shared_buffers": f"{int(shared_buffers/10**6)}MB",
+                "effective_cache_size": f"{int(effective_cache_size/10**6)}MB",
+            }
+
+            return parameters

src/charm.py

@@ -1362,6 +1362,11 @@ def update_config(self, is_creating_backup: bool = False) -> bool:
         """Updates Patroni config file based on the existence of the TLS files."""
         enable_tls = all(self.tls.get_tls_files())
 
+        # Build PostgreSQL parameters.
+        pg_parameters = self.postgresql.build_postgresql_parameters(
+            self.config["profile"], self.get_available_memory()
+        )
+
         # Update and reload configuration based on TLS files availability.
         self._patroni.render_patroni_yml_file(
             connectivity=self.unit_peer_data.get("connectivity", "on") == "on",
@@ -1370,7 +1375,7 @@ def update_config(self, is_creating_backup: bool = False) -> bool:
             backup_id=self.app_peer_data.get("restoring-backup"),
             stanza=self.app_peer_data.get("stanza"),
             restore_stanza=self.app_peer_data.get("restore-stanza"),
-            parameters=self.postgresql.build_postgresql_parameters(self.config["profile"], 0),
+            parameters=pg_parameters,
         )
         if not self._is_workload_running:
             # If Patroni/PostgreSQL has not started yet and TLS relations was initialised,
@@ -1417,6 +1422,15 @@ def _update_relation_endpoints(self) -> None:
         self.legacy_db_relation.update_endpoints()
         self.legacy_db_admin_relation.update_endpoints()
 
+    def get_available_memory(self) -> int:
+        """Returns the system available memory in bytes."""
+        with open("/proc/meminfo") as meminfo:
+            for line in meminfo:
+                if "MemTotal" in line:
+                    return int(line.split()[1]) * 1024
+
+        return 0
+
 
 if __name__ == "__main__":
     main(PostgresqlOperatorCharm)