dsdb-schema: do not reload more often than schema_reload_interval

Samba 4 use to try to reload the schema every time dsdb_get_schema was
called (which could be 20+ time per ldb request). Now we only reload at
most every xx seconds (xx being the value of dsdb:"schema_reload_interval"
 or 120). The timestamp of the last reloaded schema is kept in the
 dsdb_schema object. There is also a timestamp in the ldb_context, that
 is used by the LDAP server to know if it has to reload the schema after
 handling the request. This is used to allow that the schema will be
 immediately reload after a schemaUpdateNow request has been issued, the
 reload can't occur in the handling of the LDAP request itself because
 we have a transaction autostarted.

source4/dsdb/samdb/ldb_modules/samldb.c

@@ -4,6 +4,7 @@
    Copyright (C) Andrew Bartlett <abartlet@samba.org> 2005
    Copyright (C) Simo Sorce  2004-2008
    Copyright (C) Matthias Dieter Wallnöfer 2009-2011
+   Copyright (C) Matthieu Patou 2012
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -428,6 +429,8 @@ static int samldb_add_handle_msDS_IntId(struct samldb_ctx *ac)
 	struct ldb_context *ldb;
 	struct ldb_result *ldb_res;
 	struct ldb_dn *schema_dn;
+	struct samldb_msds_intid_persistant *msds_intid_struct;
+	struct dsdb_schema *schema;
 
 	ldb = ldb_module_get_ctx(ac->module);
 	schema_dn = ldb_get_schema_basedn(ldb);

source4/dsdb/samdb/ldb_modules/schema_load.c

@@ -49,6 +49,10 @@ static struct dsdb_schema *dsdb_schema_refresh(struct ldb_module *module, struct
 	struct dsdb_control_current_partition *ctrl;
 	struct ldb_context *ldb = ldb_module_get_ctx(module);
 	struct dsdb_schema *new_schema;
+	int interval;
+	time_t ts, lastts;
+	struct loadparm_context *lp_ctx =
+		(struct loadparm_context *)ldb_get_opaque(ldb, "loadparm");
 	
 	struct schema_load_private_data *private_data = talloc_get_type(ldb_module_get_private(module), struct schema_load_private_data);
 	if (!private_data) {
@@ -61,6 +65,14 @@ static struct dsdb_schema *dsdb_schema_refresh(struct ldb_module *module, struct
 		return schema;
 	}
 
+	lastts = schema->last_refresh;
+	ts = time(NULL);
+	interval = lpcfg_parm_int(lp_ctx, NULL, "dsdb", "schema_reload_interval", 120);
+	if (lastts > (ts - interval)) {
+		DEBUG(11, ("Less than %d seconds since last reload, returning cached version ts = %d\n", interval, (int)lastts));
+		return schema;
+	}
+
 	res = talloc_zero(schema, struct ldb_result);
 	if (res == NULL) {
 		return NULL;
@@ -84,7 +96,16 @@ static struct dsdb_schema *dsdb_schema_refresh(struct ldb_module *module, struct
 		talloc_free(res);
 		return NULL;
 	}
-	
+
+	/*
+	 * We update right now the last refresh timestamp so that if
+	 * the schema partition hasn't change we don't keep on retrying.
+	 * Otherwise if the timestamp was update only when the schema has
+	 * actually changed (and therefor completely reloaded) we would
+	 * continue to hit the database to get the highest USN.
+	 */
+	schema->last_refresh = ts;
+
 	ctrl = talloc(treq, struct dsdb_control_current_partition);
 	if (!ctrl) {
 		talloc_free(res);
@@ -130,7 +151,7 @@ static struct dsdb_schema *dsdb_schema_refresh(struct ldb_module *module, struct
 	if (ret != LDB_SUCCESS) {
 		return schema;
 	}
-	
+
 	if (is_global_schema) {
 		dsdb_make_schema_global(ldb, new_schema);
 	}
@@ -226,6 +247,7 @@ static int dsdb_schema_from_db(struct ldb_module *module, struct ldb_dn *schema_
 	ret = dsdb_set_schema(ldb, (*schema));
 
 	(*schema)->refresh_in_progress = false;
+	(*schema)->last_refresh = time(NULL);
 
 	if (ret != LDB_SUCCESS) {
 		ldb_debug_set(ldb, LDB_DEBUG_FATAL,
@@ -324,9 +346,22 @@ static int schema_load_del_transaction(struct ldb_module *module)
 
 static int schema_load_extended(struct ldb_module *module, struct ldb_request *req)
 {
+	time_t *lastts;
+	struct ldb_context *ldb = ldb_module_get_ctx(module);
+	struct dsdb_schema *schema;
+
 	if (strcmp(req->op.extended.oid, DSDB_EXTENDED_SCHEMA_UPDATE_NOW_OID) != 0) {
 		return ldb_next_request(module, req);
 	}
+	lastts = (time_t *)ldb_get_opaque(ldb, DSDB_OPAQUE_LAST_SCHEMA_UPDATE_MSG_OPAQUE_NAME);
+	if (!lastts) {
+		lastts = talloc(ldb, time_t);
+	}
+	schema = dsdb_get_schema(ldb, NULL);
+	/* Force a refresh */
+	schema->last_refresh = 0;
+	*lastts = 0;
+	ldb_set_opaque(ldb, DSDB_OPAQUE_LAST_SCHEMA_UPDATE_MSG_OPAQUE_NAME, lastts);
 
 	/* This is a no-op.  We reload as soon as we can */
 	return ldb_module_done(req, NULL, NULL, LDB_SUCCESS);

source4/dsdb/samdb/samdb.h

@@ -199,6 +199,7 @@ struct dsdb_extended_dn_store_format {
 	bool store_extended_dn_in_ldb;
 };
 
+#define DSDB_OPAQUE_LAST_SCHEMA_UPDATE_MSG_OPAQUE_NAME "DSDB_OPAQUE_LAST_SCHEMA_UPDATE"
 #define DSDB_OPAQUE_PARTITION_MODULE_MSG_OPAQUE_NAME "DSDB_OPAQUE_PARTITION_MODULE_MSG"
 
 /* this takes a struct dsdb_fsmo_extended_op */

source4/dsdb/schema/schema.h

@@ -245,6 +245,7 @@ struct dsdb_schema {
 	struct ldb_module *loaded_from_module;
 	struct dsdb_schema *(*refresh_fn)(struct ldb_module *module, struct dsdb_schema *schema, bool is_global_schema);
 	bool refresh_in_progress;
+	time_t last_refresh;
 	/* an 'opaque' sequence number that the reload function may also wish to use */
 	uint64_t reload_seq_number;
 

source4/ldap_server/ldap_backend.c

@@ -1162,6 +1162,9 @@ NTSTATUS ldapsrv_do_call(struct ldapsrv_call *call)
 {
 	unsigned int i;
 	struct ldap_message *msg = call->request;
+	struct ldb_context *samdb = call->conn->ldb;
+	NTSTATUS status;
+	time_t *lastts;
 	/* Check for undecoded critical extensions */
 	for (i=0; msg->controls && msg->controls[i]; i++) {
 		if (!msg->controls_decoded[i] && 
@@ -1180,9 +1183,11 @@ NTSTATUS ldapsrv_do_call(struct ldapsrv_call *call)
 	case LDAP_TAG_SearchRequest:
 		return ldapsrv_SearchRequest(call);
 	case LDAP_TAG_ModifyRequest:
-		return ldapsrv_ModifyRequest(call);
+		status = ldapsrv_ModifyRequest(call);
+		break;
 	case LDAP_TAG_AddRequest:
-		return ldapsrv_AddRequest(call);
+		status = ldapsrv_AddRequest(call);
+		break;
 	case LDAP_TAG_DelRequest:
 		return ldapsrv_DelRequest(call);
 	case LDAP_TAG_ModifyDNRequest:
@@ -1196,4 +1201,20 @@ NTSTATUS ldapsrv_do_call(struct ldapsrv_call *call)
 	default:
 		return ldapsrv_unwilling(call, LDAP_PROTOCOL_ERROR);
 	}
+
+	if (NT_STATUS_IS_OK(status)) {
+		lastts = (time_t *)ldb_get_opaque(samdb, DSDB_OPAQUE_LAST_SCHEMA_UPDATE_MSG_OPAQUE_NAME);
+		if (lastts && !*lastts) {
+			DEBUG(10, ("Schema update now was requested, fullfilling the request ts = %d\n", lastts));
+			/*
+			* Just requesting the schema will do the trick
+			* as the delay for reload is experied, we will have a reload
+			* from the schema as expected as we are not yet in a transaction!
+			*/
+			dsdb_get_schema(samdb, NULL);
+			*lastts = time(NULL);
+			ldb_set_opaque(samdb, DSDB_OPAQUE_LAST_SCHEMA_UPDATE_MSG_OPAQUE_NAME, lastts);
+		}
+	}
+	return status;
 }