X-Git-Url: https://git.tokkee.org/?p=sysdb.git;a=blobdiff_plain;f=src%2Fcore%2Fplugin.c;h=b3f00bd655504075b97c5f158b8c45a8c0d20d05;hp=7404b036392ecd5c76899009dd7f515ff9d87d8e;hb=dcf7802ad0958d4752b2c13f70e2fdf345d3509f;hpb=af74f327da5e6ebe01d5e5e6f8fa19646e203eed

diff --git a/src/core/plugin.c b/src/core/plugin.c
index 7404b03..b3f00bd 100644
--- a/src/core/plugin.c
+++ b/src/core/plugin.c
@@ -80,31 +80,47 @@ typedef struct {
 	void *cb_callback;
 	sdb_object_t *cb_user_data;
 	ctx_t *cb_ctx;
-} sdb_plugin_cb_t;
-#define SDB_PLUGIN_CB_INIT { SDB_OBJECT_INIT, \
+} callback_t;
+#define CB_INIT { SDB_OBJECT_INIT, \
 	/* callback = */ NULL, /* user_data = */ NULL, \
 	SDB_PLUGIN_CTX_INIT }
-#define SDB_PLUGIN_CB(obj) ((sdb_plugin_cb_t *)(obj))
-#define SDB_CONST_PLUGIN_CB(obj) ((const sdb_plugin_cb_t *)(obj))
+#define CB(obj) ((callback_t *)(obj))
+#define CONST_CB(obj) ((const callback_t *)(obj))
 
 typedef struct {
-	sdb_plugin_cb_t super;
+	callback_t super;
 #define ccb_callback super.cb_callback
 #define ccb_user_data super.cb_user_data
 #define ccb_ctx super.cb_ctx
 	sdb_time_t ccb_interval;
 	sdb_time_t ccb_next_update;
-} sdb_plugin_collector_cb_t;
-#define SDB_PLUGIN_CCB(obj) ((sdb_plugin_collector_cb_t *)(obj))
-#define SDB_CONST_PLUGIN_CCB(obj) ((const sdb_plugin_collector_cb_t *)(obj))
+} collector_t;
+#define CCB(obj) ((collector_t *)(obj))
+#define CONST_CCB(obj) ((const collector_t *)(obj))
 
 typedef struct {
-	sdb_object_t super;
+	callback_t super; /* cb_callback will always be NULL */
+#define w_user_data super.cb_user_data
+#define w_ctx super.cb_ctx
 	sdb_store_writer_t impl;
-	sdb_object_t *user_data;
-	ctx_t *ctx;
-} sdb_plugin_writer_t;
-#define SDB_PLUGIN_WRITER(obj) ((sdb_plugin_writer_t *)(obj))
+} writer_t;
+#define WRITER(obj) ((writer_t *)(obj))
+
+typedef struct {
+	callback_t super; /* cb_callback will always be NULL */
+#define r_user_data super.cb_user_data
+#define r_ctx super.cb_ctx
+	sdb_store_reader_t impl;
+} reader_t;
+#define READER(obj) ((reader_t *)(obj))
+
+typedef struct {
+	callback_t super; /* cb_callback will always be NULL */
+#define ts_user_data super.cb_user_data
+#define ts_ctx super.cb_ctx
+	sdb_timeseries_fetcher_t impl;
+} ts_fetcher_t;
+#define TS_FETCHER(obj) ((ts_fetcher_t *)(obj))
 
 /*
  * private variables
@@ -125,8 +141,9 @@ static sdb_llist_t      *collector_list = NULL;
 static sdb_llist_t      *cname_list = NULL;
 static sdb_llist_t      *shutdown_list = NULL;
 static sdb_llist_t      *log_list = NULL;
-static sdb_llist_t      *ts_fetcher_list = NULL;
+static sdb_llist_t      *timeseries_fetcher_list = NULL;
 static sdb_llist_t      *writer_list = NULL;
+static sdb_llist_t      *reader_list = NULL;
 
 static struct {
 	const char   *type;
@@ -138,8 +155,9 @@ static struct {
 	{ "cname",              &cname_list },
 	{ "shutdown",           &shutdown_list },
 	{ "log",                &log_list },
-	{ "timeseries fetcher", &ts_fetcher_list },
+	{ "timeseries fetcher", &timeseries_fetcher_list },
 	{ "store writer",       &writer_list },
+	{ "store reader",       &reader_list },
 };
 
 /*
@@ -181,10 +199,8 @@ ctx_key_init(void)
 static int
 plugin_cmp_next_update(const sdb_object_t *a, const sdb_object_t *b)
 {
-	const sdb_plugin_collector_cb_t *ccb1
-		= (const sdb_plugin_collector_cb_t *)a;
-	const sdb_plugin_collector_cb_t *ccb2
-		= (const sdb_plugin_collector_cb_t *)b;
+	const collector_t *ccb1 = (const collector_t *)a;
+	const collector_t *ccb2 = (const collector_t *)b;
 
 	assert(ccb1 && ccb2);
 
@@ -196,7 +212,7 @@ plugin_cmp_next_update(const sdb_object_t *a, const sdb_object_t *b)
 static int
 plugin_lookup_by_name(const sdb_object_t *obj, const void *id)
 {
-	const sdb_plugin_cb_t *cb = SDB_CONST_PLUGIN_CB(obj);
+	const callback_t *cb = CONST_CB(obj);
 	const char *name = id;
 
 	assert(cb && id);
@@ -225,18 +241,17 @@ plugin_unregister_by_name(const char *plugin_name)
 		sdb_llist_t *list = *all_lists[i].list;
 
 		while (1) {
-			sdb_plugin_cb_t *cb;
+			callback_t *cb;
 
-			cb = SDB_PLUGIN_CB(sdb_llist_remove(list,
+			cb = CB(sdb_llist_remove(list,
 						plugin_lookup_by_name, plugin_name));
 			if (! cb)
 				break;
 
 			assert(cb->cb_ctx);
 
-			sdb_log(SDB_LOG_INFO, "core: Unregistering "
-					"%s callback '%s' (module %s)", type, cb->super.name,
-					cb->cb_ctx->info.plugin_name);
+			sdb_log(SDB_LOG_INFO, "Unregistering %s callback '%s' (module %s)",
+					type, cb->super.name, cb->cb_ctx->info.plugin_name);
 			sdb_object_deref(SDB_OBJ(cb));
 		}
 	}
@@ -251,25 +266,80 @@ plugin_unregister_by_name(const char *plugin_name)
 	/* else: other callbacks still reference it */
 } /* plugin_unregister_by_name */
 
-static void
-plugin_unregister_all(void)
+/*
+ * store writer wrapper for performing database queries:
+ * It wraps another store writer, adding extra logic as needed.
+ */
+
+typedef struct {
+	sdb_object_t super;
+	sdb_store_writer_t *w;
+	sdb_object_t *ud;
+	sdb_query_opts_t opts;
+} query_writer_t;
+#define QUERY_WRITER_INIT(w, ud) { \
+	SDB_OBJECT_INIT, \
+	(w), (ud), \
+	SDB_DEFAULT_QUERY_OPTS \
+}
+#define QUERY_WRITER(obj) ((query_writer_t *)(obj))
+
+static int
+query_store_host(sdb_store_host_t *host, sdb_object_t *user_data)
 {
-	size_t i;
+	query_writer_t *qw = QUERY_WRITER(user_data);
+	return qw->w->store_host(host, qw->ud);
+} /* query_store_host */
 
-	for (i = 0; i < SDB_STATIC_ARRAY_LEN(all_lists); ++i) {
-		const char  *type =  all_lists[i].type;
-		sdb_llist_t *list = *all_lists[i].list;
+static int
+query_store_service(sdb_store_service_t *service, sdb_object_t *user_data)
+{
+	query_writer_t *qw = QUERY_WRITER(user_data);
+	return qw->w->store_service(service, qw->ud);
+} /* query_store_service */
 
-		size_t len = sdb_llist_len(list);
+static int
+query_store_metric(sdb_store_metric_t *metric, sdb_object_t *user_data)
+{
+	query_writer_t *qw = QUERY_WRITER(user_data);
+	sdb_timeseries_info_t *infos[metric->stores_num];
+	sdb_metric_store_t stores[metric->stores_num];
 
-		if (! len)
-			continue;
+	const sdb_metric_store_t *orig_stores = metric->stores;
+	int status;
+	size_t i;
 
-		sdb_llist_clear(list);
-		sdb_log(SDB_LOG_INFO, "core: Unregistered %zu %s callback%s",
-				len, type, len == 1 ? "" : "s");
+	if (! qw->opts.describe_timeseries)
+		/* nothing further to do */
+		return qw->w->store_metric(metric, qw->ud);
+
+	for (i = 0; i < metric->stores_num; i++) {
+		sdb_metric_store_t *s = stores + i;
+		*s = metric->stores[i];
+		infos[i] = sdb_plugin_describe_timeseries(s->type, s->id);
+		s->info = infos[i];
 	}
-} /* plugin_unregister_all */
+
+	metric->stores = stores;
+	status = qw->w->store_metric(metric, qw->ud);
+	metric->stores = orig_stores;
+
+	for (i = 0; i < metric->stores_num; i++)
+		sdb_timeseries_info_destroy(infos[i]);
+	return status;
+} /* query_store_metric */
+
+static int
+query_store_attribute(sdb_store_attribute_t *attr, sdb_object_t *user_data)
+{
+	query_writer_t *qw = QUERY_WRITER(user_data);
+	return qw->w->store_attribute(attr, qw->ud);
+} /* query_store_attribute */
+
+static sdb_store_writer_t query_writer = {
+	query_store_host, query_store_service,
+	query_store_metric, query_store_attribute,
+};
 
 /*
  * private types
@@ -297,13 +367,12 @@ ctx_destroy(sdb_object_t *obj)
 	if (ctx->handle) {
 		const char *err;
 
-		sdb_log(SDB_LOG_INFO, "core: Unloading module %s",
-				ctx->info.plugin_name);
+		sdb_log(SDB_LOG_INFO, "Unloading module %s", ctx->info.plugin_name);
 
 		lt_dlerror();
 		lt_dlclose(ctx->handle);
 		if ((err = lt_dlerror()))
-			sdb_log(SDB_LOG_WARNING, "core: Failed to unload module %s: %s",
+			sdb_log(SDB_LOG_WARNING, "Failed to unload module %s: %s",
 					ctx->info.plugin_name, err);
 	}
 
@@ -357,33 +426,48 @@ ctx_create(const char *name)
 	return ctx;
 } /* ctx_create */
 
-static int
-plugin_cb_init(sdb_object_t *obj, va_list ap)
+/*
+ * plugin_init_ok:
+ * Checks whether the registration of a new plugin identified by 'obj' is
+ * okay. It consumes the first two arguments of 'ap'.
+ */
+static bool
+plugin_init_ok(sdb_object_t *obj, va_list ap)
 {
 	sdb_llist_t **list = va_arg(ap, sdb_llist_t **);
-	const char   *type = va_arg(ap, const char *);
-	void     *callback = va_arg(ap, void *);
-	sdb_object_t   *ud = va_arg(ap, sdb_object_t *);
+	const char *type = va_arg(ap, const char *);
 
-	assert(list);
-	assert(type);
-	assert(obj);
+	assert(list); assert(type);
 
 	if (sdb_llist_search_by_name(*list, obj->name)) {
-		sdb_log(SDB_LOG_WARNING, "core: %s callback '%s' "
-				"has already been registered. Ignoring newly "
-				"registered version.", type, obj->name);
-		return -1;
+		sdb_log(SDB_LOG_WARNING, "%s callback '%s' has already been "
+				"registered. Ignoring newly registered version.",
+				type, obj->name);
+		return 0;
 	}
+	return 1;
+} /* plugin_init_ok */
+
+static int
+plugin_cb_init(sdb_object_t *obj, va_list ap)
+{
+	void *callback;
+	sdb_object_t *ud;
+
+	if (! plugin_init_ok(obj, ap))
+		return -1;
+
+	callback = va_arg(ap, void *);
+	ud = va_arg(ap, sdb_object_t *);
 
 	/* cb_ctx may be NULL if the plugin was not registered by a plugin */
 
-	SDB_PLUGIN_CB(obj)->cb_callback = callback;
-	SDB_PLUGIN_CB(obj)->cb_ctx      = ctx_get();
-	sdb_object_ref(SDB_OBJ(SDB_PLUGIN_CB(obj)->cb_ctx));
+	CB(obj)->cb_callback = callback;
+	CB(obj)->cb_ctx      = ctx_get();
+	sdb_object_ref(SDB_OBJ(CB(obj)->cb_ctx));
 
 	sdb_object_ref(ud);
-	SDB_PLUGIN_CB(obj)->cb_user_data = ud;
+	CB(obj)->cb_user_data = ud;
 	return 0;
 } /* plugin_cb_init */
 
@@ -391,19 +475,19 @@ static void
 plugin_cb_destroy(sdb_object_t *obj)
 {
 	assert(obj);
-	sdb_object_deref(SDB_PLUGIN_CB(obj)->cb_user_data);
-	sdb_object_deref(SDB_OBJ(SDB_PLUGIN_CB(obj)->cb_ctx));
+	sdb_object_deref(CB(obj)->cb_user_data);
+	sdb_object_deref(SDB_OBJ(CB(obj)->cb_ctx));
 } /* plugin_cb_destroy */
 
-static sdb_type_t sdb_plugin_cb_type = {
-	sizeof(sdb_plugin_cb_t),
+static sdb_type_t callback_type = {
+	sizeof(callback_t),
 
 	plugin_cb_init,
 	plugin_cb_destroy
 };
 
-static sdb_type_t sdb_plugin_collector_cb_type = {
-	sizeof(sdb_plugin_collector_cb_t),
+static sdb_type_t collector_type = {
+	sizeof(collector_t),
 
 	plugin_cb_init,
 	plugin_cb_destroy
@@ -412,34 +496,31 @@ static sdb_type_t sdb_plugin_collector_cb_type = {
 static int
 plugin_writer_init(sdb_object_t *obj, va_list ap)
 {
-	sdb_store_writer_t *impl = va_arg(ap, sdb_store_writer_t *);
-	sdb_object_t       *ud   = va_arg(ap, sdb_object_t *);
+	sdb_store_writer_t *impl;
+	sdb_object_t *ud;
+
+	if (! plugin_init_ok(obj, ap))
+		return -1;
 
+	impl = va_arg(ap, sdb_store_writer_t *);
+	ud = va_arg(ap, sdb_object_t *);
 	assert(impl);
 
 	if ((! impl->store_host) || (! impl->store_service)
-			|| (! impl->store_metric) || (! impl->store_attribute)
-			|| (! impl->store_service_attr) || (! impl->store_metric_attr)) {
-		sdb_log(SDB_LOG_ERR, "core: store writer callback '%s' "
-				"does not fully implement the writer interface.",
-				obj->name);
-		return -1;
-	}
-	if (sdb_llist_search_by_name(writer_list, obj->name)) {
-		sdb_log(SDB_LOG_WARNING, "core: store writer callback '%s' "
-				"has already been registered. Ignoring newly "
-				"registered version.", obj->name);
+			|| (! impl->store_metric) || (! impl->store_attribute)) {
+		sdb_log(SDB_LOG_ERR, "store writer callback '%s' does not fully "
+				"implement the writer interface.", obj->name);
 		return -1;
 	}
 
-	/* ctx may be NULL if the plugin was not registered by a plugin */
+	/* ctx may be NULL if the callback was not registered by a plugin */
 
-	SDB_PLUGIN_WRITER(obj)->impl = *impl;
-	SDB_PLUGIN_WRITER(obj)->ctx  = ctx_get();
-	sdb_object_ref(SDB_OBJ(SDB_PLUGIN_WRITER(obj)->ctx));
+	WRITER(obj)->impl = *impl;
+	WRITER(obj)->w_ctx  = ctx_get();
+	sdb_object_ref(SDB_OBJ(WRITER(obj)->w_ctx));
 
 	sdb_object_ref(ud);
-	SDB_PLUGIN_WRITER(obj)->user_data = ud;
+	WRITER(obj)->w_user_data = ud;
 	return 0;
 } /* plugin_writer_init */
 
@@ -447,17 +528,107 @@ static void
 plugin_writer_destroy(sdb_object_t *obj)
 {
 	assert(obj);
-	sdb_object_deref(SDB_PLUGIN_WRITER(obj)->user_data);
-	sdb_object_deref(SDB_OBJ(SDB_PLUGIN_WRITER(obj)->ctx));
+	sdb_object_deref(WRITER(obj)->w_user_data);
+	sdb_object_deref(SDB_OBJ(WRITER(obj)->w_ctx));
 } /* plugin_writer_destroy */
 
-static sdb_type_t sdb_plugin_writer_type = {
-	sizeof(sdb_plugin_writer_t),
+static sdb_type_t writer_type = {
+	sizeof(writer_t),
 
 	plugin_writer_init,
 	plugin_writer_destroy
 };
 
+static int
+plugin_reader_init(sdb_object_t *obj, va_list ap)
+{
+	sdb_store_reader_t *impl;
+	sdb_object_t *ud;
+
+	if (! plugin_init_ok(obj, ap))
+		return -1;
+
+	impl = va_arg(ap, sdb_store_reader_t *);
+	ud = va_arg(ap, sdb_object_t *);
+	assert(impl);
+
+	if ((! impl->prepare_query) || (! impl->execute_query)) {
+		sdb_log(SDB_LOG_ERR, "store reader callback '%s' does not fully "
+				"implement the reader interface.", obj->name);
+		return -1;
+	}
+
+	/* ctx may be NULL if the callback was not registered by a plugin */
+
+	READER(obj)->impl = *impl;
+	READER(obj)->r_ctx  = ctx_get();
+	sdb_object_ref(SDB_OBJ(READER(obj)->r_ctx));
+
+	sdb_object_ref(ud);
+	READER(obj)->r_user_data = ud;
+	return 0;
+} /* plugin_reader_init */
+
+static void
+plugin_reader_destroy(sdb_object_t *obj)
+{
+	assert(obj);
+	sdb_object_deref(READER(obj)->r_user_data);
+	sdb_object_deref(SDB_OBJ(READER(obj)->r_ctx));
+} /* plugin_reader_destroy */
+
+static sdb_type_t reader_type = {
+	sizeof(reader_t),
+
+	plugin_reader_init,
+	plugin_reader_destroy
+};
+
+static int
+plugin_ts_fetcher_init(sdb_object_t *obj, va_list ap)
+{
+	sdb_timeseries_fetcher_t *impl;
+	sdb_object_t *ud;
+
+	if (! plugin_init_ok(obj, ap))
+		return -1;
+
+	impl = va_arg(ap, sdb_timeseries_fetcher_t *);
+	ud = va_arg(ap, sdb_object_t *);
+	assert(impl);
+
+	if ((! impl->describe) || (! impl->fetch)) {
+		sdb_log(SDB_LOG_ERR, "timeseries fetcher callback '%s' does not fully "
+				"implement the interface.", obj->name);
+		return -1;
+	}
+
+	/* ctx may be NULL if the callback was not registered by a plugin */
+
+	TS_FETCHER(obj)->impl = *impl;
+	TS_FETCHER(obj)->ts_ctx  = ctx_get();
+	sdb_object_ref(SDB_OBJ(TS_FETCHER(obj)->ts_ctx));
+
+	sdb_object_ref(ud);
+	TS_FETCHER(obj)->ts_user_data = ud;
+	return 0;
+} /* plugin_ts_fetcher_init */
+
+static void
+plugin_ts_fetcher_destroy(sdb_object_t *obj)
+{
+	assert(obj);
+	sdb_object_deref(TS_FETCHER(obj)->ts_user_data);
+	sdb_object_deref(SDB_OBJ(TS_FETCHER(obj)->ts_ctx));
+} /* plugin_ts_fetcher_destroy */
+
+static sdb_type_t ts_fetcher_type = {
+	sizeof(ts_fetcher_t),
+
+	plugin_ts_fetcher_init,
+	plugin_ts_fetcher_destroy
+};
+
 static int
 module_init(const char *name, lt_dlhandle lh, sdb_plugin_info_t *info)
 {
@@ -466,15 +637,14 @@ module_init(const char *name, lt_dlhandle lh, sdb_plugin_info_t *info)
 
 	mod_init = (int (*)(sdb_plugin_info_t *))lt_dlsym(lh, "sdb_module_init");
 	if (! mod_init) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
+		sdb_log(SDB_LOG_ERR, "Failed to load plugin '%s': "
 				"could not find symbol 'sdb_module_init'", name);
 		return -1;
 	}
 
 	status = mod_init(info);
 	if (status) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to initialize "
-				"module '%s'", name);
+		sdb_log(SDB_LOG_ERR, "Failed to initialize module '%s'", name);
 		plugin_unregister_by_name(name);
 		return -1;
 	}
@@ -516,7 +686,7 @@ module_load(const char *basedir, const char *name,
 
 	if (access(filename, R_OK)) {
 		char errbuf[1024];
-		sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s' (%s): %s",
+		sdb_log(SDB_LOG_ERR, "Failed to load plugin '%s' (%s): %s",
 				name, filename, sdb_strerror(errno, errbuf, sizeof(errbuf)));
 		return -1;
 	}
@@ -526,18 +696,18 @@ module_load(const char *basedir, const char *name,
 
 	lh = lt_dlopen(filename);
 	if (! lh) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': %s"
+		sdb_log(SDB_LOG_ERR, "Failed to load plugin '%s': %s"
 				"The most common cause for this problem are missing "
 				"dependencies.\n", name, lt_dlerror());
 		return -1;
 	}
 
 	if (ctx_get())
-		sdb_log(SDB_LOG_WARNING, "core: Discarding old plugin context");
+		sdb_log(SDB_LOG_WARNING, "Discarding old plugin context");
 
 	ctx = ctx_create(name);
 	if (! ctx) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to initialize plugin context");
+		sdb_log(SDB_LOG_ERR, "Failed to initialize plugin context");
 		return -1;
 	}
 
@@ -550,26 +720,26 @@ module_load(const char *basedir, const char *name,
 
 	if ((status = module_init(name, lh, &ctx->info))) {
 		sdb_object_deref(SDB_OBJ(ctx));
+		ctx_set(NULL);
 		return status;
 	}
 
 	/* compare minor version */
 	if ((ctx->info.version < 0)
 			|| ((int)(ctx->info.version / 100) != (int)(SDB_VERSION / 100)))
-		sdb_log(SDB_LOG_WARNING, "core: WARNING: version of "
-				"plugin '%s' (%i.%i.%i) does not match our version "
-				"(%i.%i.%i); this might cause problems",
-				name, SDB_VERSION_DECODE(ctx->info.version),
+		sdb_log(SDB_LOG_WARNING, "WARNING: plugin version (%i.%i.%i) "
+				"does not match core version (%i.%i.%i); "
+				"this might cause problems",
+				SDB_VERSION_DECODE(ctx->info.version),
 				SDB_VERSION_DECODE(SDB_VERSION));
 
 	sdb_llist_append(all_plugins, SDB_OBJ(ctx));
 
-	sdb_log(SDB_LOG_INFO, "core: Successfully loaded "
-			"plugin %s v%i (%s)", ctx->info.plugin_name,
-			ctx->info.plugin_version,
+	/* log messages will be prefixed by the plugin name */
+	sdb_log(SDB_LOG_INFO, "Successfully loaded "
+			"version %i (%s)", ctx->info.plugin_version,
 			INFO_GET(&ctx->info, description));
-	sdb_log(SDB_LOG_INFO, "core: Plugin %s: %s, License: %s",
-			ctx->info.plugin_name,
+	sdb_log(SDB_LOG_INFO, "%s, License: %s",
 			INFO_GET(&ctx->info, copyright),
 			INFO_GET(&ctx->info, license));
 
@@ -594,12 +764,12 @@ plugin_get_name(const char *name, char *buf, size_t bufsize)
 } /* plugin_get_name */
 
 static int
-plugin_add_callback(sdb_llist_t **list, const char *type,
-		const char *name, void *callback, sdb_object_t *user_data)
+plugin_add_impl(sdb_llist_t **list, sdb_type_t T, const char *type,
+		const char *name, void *impl, sdb_object_t *user_data)
 {
 	sdb_object_t *obj;
 
-	if ((! name) || (! callback))
+	if ((! name) || (! impl))
 		return -1;
 
 	assert(list);
@@ -609,8 +779,7 @@ plugin_add_callback(sdb_llist_t **list, const char *type,
 	if (! *list)
 		return -1;
 
-	obj = sdb_object_create(name, sdb_plugin_cb_type,
-			list, type, callback, user_data);
+	obj = sdb_object_create(name, T, list, type, impl, user_data);
 	if (! obj)
 		return -1;
 
@@ -622,10 +791,129 @@ plugin_add_callback(sdb_llist_t **list, const char *type,
 	/* pass control to the list */
 	sdb_object_deref(obj);
 
-	sdb_log(SDB_LOG_INFO, "core: Registered %s callback '%s'.",
-			type, name);
+	sdb_log(SDB_LOG_INFO, "Registered %s callback '%s'.", type, name);
 	return 0;
-} /* plugin_add_callback */
+} /* plugin_add_impl */
+
+/*
+ * object meta-data
+ */
+
+typedef struct {
+	int obj_type;
+	sdb_time_t last_update;
+	sdb_time_t interval;
+} interval_fetcher_t;
+
+static int
+interval_fetcher_host(sdb_store_host_t *host, sdb_object_t *user_data)
+{
+	interval_fetcher_t *lu = SDB_OBJ_WRAPPER(user_data)->data;
+	lu->obj_type = SDB_HOST;
+	lu->last_update = host->last_update;
+	return 0;
+} /* interval_fetcher_host */
+
+static int
+interval_fetcher_service(sdb_store_service_t *svc, sdb_object_t *user_data)
+{
+	interval_fetcher_t *lu = SDB_OBJ_WRAPPER(user_data)->data;
+	lu->obj_type = SDB_SERVICE;
+	lu->last_update = svc->last_update;
+	return 0;
+} /* interval_fetcher_service */
+
+static int
+interval_fetcher_metric(sdb_store_metric_t *metric, sdb_object_t *user_data)
+{
+	interval_fetcher_t *lu = SDB_OBJ_WRAPPER(user_data)->data;
+	lu->obj_type = SDB_METRIC;
+	lu->last_update = metric->last_update;
+	return 0;
+} /* interval_fetcher_metric */
+
+static int
+interval_fetcher_attr(sdb_store_attribute_t *attr, sdb_object_t *user_data)
+{
+	interval_fetcher_t *lu = SDB_OBJ_WRAPPER(user_data)->data;
+	lu->obj_type = SDB_ATTRIBUTE;
+	lu->last_update = attr->last_update;
+	return 0;
+} /* interval_fetcher_attr */
+
+static sdb_store_writer_t interval_fetcher = {
+	interval_fetcher_host, interval_fetcher_service,
+	interval_fetcher_metric, interval_fetcher_attr,
+};
+
+static int
+get_interval(int obj_type, const char *hostname,
+		int parent_type, const char *parent, const char *name,
+		sdb_time_t last_update, sdb_time_t *interval_out)
+{
+	sdb_ast_fetch_t fetch = SDB_AST_FETCH_INIT;
+	char hn[hostname ? strlen(hostname) + 1 : 1];
+	char pn[parent ? strlen(parent) + 1 : 1];
+	char n[strlen(name) + 1];
+	int status;
+
+	interval_fetcher_t lu = { 0, 0, 0 };
+	sdb_object_wrapper_t obj = SDB_OBJECT_WRAPPER_STATIC(&lu);
+	sdb_time_t interval;
+
+	assert(name);
+
+	if (hostname)
+		strncpy(hn, hostname, sizeof(hn));
+	if (parent)
+		strncpy(pn, parent, sizeof(pn));
+	strncpy(n, name, sizeof(n));
+
+	fetch.obj_type = obj_type;
+	fetch.hostname = hostname ? hn : NULL;
+	fetch.parent_type = parent_type;
+	fetch.parent = parent ? pn : NULL;
+	fetch.name = n;
+
+	status = sdb_plugin_query(SDB_AST_NODE(&fetch),
+			&interval_fetcher, SDB_OBJ(&obj), NULL, NULL);
+	if ((status < 0) || (lu.obj_type != obj_type) || (lu.last_update == 0)) {
+		*interval_out = 0;
+		return 0;
+	}
+
+	if (lu.last_update >= last_update) {
+		if (lu.last_update > last_update)
+			sdb_log(SDB_LOG_DEBUG, "Cannot update %s '%s' - "
+					"value too old (%"PRIsdbTIME" < %"PRIsdbTIME")",
+					SDB_STORE_TYPE_TO_NAME(obj_type), name,
+					lu.last_update, last_update);
+		*interval_out = lu.interval;
+		return 1;
+	}
+
+	interval = last_update - lu.last_update;
+	if (lu.interval && interval)
+		interval = (sdb_time_t)((0.9 * (double)lu.interval)
+				+ (0.1 * (double)interval));
+	*interval_out = interval;
+	return 0;
+} /* get_interval */
+
+static void
+get_backend(char **backends, size_t *backends_num)
+{
+	const sdb_plugin_info_t *info;
+
+	info = sdb_plugin_current();
+	if ((! info) || (! info->plugin_name) || (! *info->plugin_name)) {
+		*backends_num = 0;
+		return;
+	}
+
+	backends[0] = info->plugin_name;
+	*backends_num = 1;
+} /* get_backend */
 
 /*
  * public API
@@ -644,7 +932,7 @@ sdb_plugin_load(const char *basedir, const char *name,
 
 	if (! all_plugins) {
 		if (! (all_plugins = sdb_llist_create())) {
-			sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
+			sdb_log(SDB_LOG_ERR, "Failed to load plugin '%s': "
 					"internal error while creating linked list", name);
 			return -1;
 		}
@@ -658,13 +946,14 @@ sdb_plugin_load(const char *basedir, const char *name,
 			ctx_t *old_ctx = ctx_set(ctx);
 
 			status = module_init(ctx->info.plugin_name, ctx->handle, NULL);
+			ctx_set(old_ctx);
 			if (status)
 				return status;
 
-			sdb_log(SDB_LOG_INFO, "core: Successfully reloaded plugin "
+			ctx_set(old_ctx);
+			sdb_log(SDB_LOG_INFO, "Successfully reloaded plugin "
 					"'%s' (%s)", ctx->info.plugin_name,
 					INFO_GET(&ctx->info, description));
-			ctx_set(old_ctx);
 		}
 		++ctx->use_cnt;
 		return 0;
@@ -738,12 +1027,12 @@ sdb_plugin_register_config(sdb_plugin_config_cb callback)
 	ctx_t *ctx = ctx_get();
 
 	if (! ctx) {
-		sdb_log(SDB_LOG_ERR, "core: Invalid attempt to register a "
+		sdb_log(SDB_LOG_ERR, "Invalid attempt to register a "
 				"config callback from outside a plugin");
 		return -1;
 	}
-	return plugin_add_callback(&config_list, "init", ctx->info.plugin_name,
-			(void *)callback, NULL);
+	return plugin_add_impl(&config_list, callback_type, "config",
+			ctx->info.plugin_name, (void *)callback, NULL);
 } /* sdb_plugin_register_config */
 
 int
@@ -751,7 +1040,7 @@ sdb_plugin_register_init(const char *name, sdb_plugin_init_cb callback,
 		sdb_object_t *user_data)
 {
 	char cb_name[1024];
-	return plugin_add_callback(&init_list, "init",
+	return plugin_add_impl(&init_list, callback_type, "init",
 			plugin_get_name(name, cb_name, sizeof(cb_name)),
 			(void *)callback, user_data);
 } /* sdb_plugin_register_init */
@@ -761,7 +1050,7 @@ sdb_plugin_register_shutdown(const char *name, sdb_plugin_shutdown_cb callback,
 		sdb_object_t *user_data)
 {
 	char cb_name[1024];
-	return plugin_add_callback(&shutdown_list, "shutdown",
+	return plugin_add_impl(&shutdown_list, callback_type, "shutdown",
 			plugin_get_name(name, cb_name, sizeof(cb_name)),
 			(void *)callback, user_data);
 } /* sdb_plugin_register_shutdown */
@@ -771,7 +1060,7 @@ sdb_plugin_register_log(const char *name, sdb_plugin_log_cb callback,
 		sdb_object_t *user_data)
 {
 	char cb_name[1024];
-	return plugin_add_callback(&log_list, "log",
+	return plugin_add_impl(&log_list, callback_type, "log",
 			plugin_get_name(name, cb_name, sizeof(cb_name)),
 			callback, user_data);
 } /* sdb_plugin_register_log */
@@ -781,7 +1070,7 @@ sdb_plugin_register_cname(const char *name, sdb_plugin_cname_cb callback,
 		sdb_object_t *user_data)
 {
 	char cb_name[1024];
-	return plugin_add_callback(&cname_list, "cname",
+	return plugin_add_impl(&cname_list, callback_type, "cname",
 			plugin_get_name(name, cb_name, sizeof(cb_name)),
 			callback, user_data);
 } /* sdb_plugin_register_cname */
@@ -803,30 +1092,29 @@ sdb_plugin_register_collector(const char *name, sdb_plugin_collector_cb callback
 
 	plugin_get_name(name, cb_name, sizeof(cb_name));
 
-	obj = sdb_object_create(cb_name, sdb_plugin_collector_cb_type,
+	obj = sdb_object_create(cb_name, collector_type,
 			&collector_list, "collector", callback, user_data);
 	if (! obj)
 		return -1;
 
 	if (interval)
-		SDB_PLUGIN_CCB(obj)->ccb_interval = *interval;
+		CCB(obj)->ccb_interval = *interval;
 	else {
 		ctx_t *ctx = ctx_get();
 
 		if (! ctx) {
-			sdb_log(SDB_LOG_ERR, "core: Cannot determine interval "
-					"for collector %s; none specified and no plugin "
-					"context found", cb_name);
+			sdb_log(SDB_LOG_ERR, "Cannot determine interval for collector %s; "
+					"none specified and no plugin context found", cb_name);
 			return -1;
 		}
 
-		SDB_PLUGIN_CCB(obj)->ccb_interval = ctx->public.interval;
+		CCB(obj)->ccb_interval = ctx->public.interval;
 	}
 
-	if (! (SDB_PLUGIN_CCB(obj)->ccb_next_update = sdb_gettime())) {
+	if (! (CCB(obj)->ccb_next_update = sdb_gettime())) {
 		char errbuf[1024];
-		sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
-				"time: %s", sdb_strerror(errno, errbuf, sizeof(errbuf)));
+		sdb_log(SDB_LOG_ERR, "Failed to determine current time: %s",
+				sdb_strerror(errno, errbuf, sizeof(errbuf)));
 		sdb_object_deref(obj);
 		return -1;
 	}
@@ -840,54 +1128,59 @@ sdb_plugin_register_collector(const char *name, sdb_plugin_collector_cb callback
 	/* pass control to the list */
 	sdb_object_deref(obj);
 
-	sdb_log(SDB_LOG_INFO, "core: Registered collector callback '%s' "
+	sdb_log(SDB_LOG_INFO, "Registered collector callback '%s' "
 			"(interval = %.3fs).", cb_name,
-			SDB_TIME_TO_DOUBLE(SDB_PLUGIN_CCB(obj)->ccb_interval));
+			SDB_TIME_TO_DOUBLE(CCB(obj)->ccb_interval));
 	return 0;
 } /* sdb_plugin_register_collector */
 
 int
-sdb_plugin_register_ts_fetcher(const char *name,
-		sdb_plugin_fetch_ts_cb callback, sdb_object_t *user_data)
+sdb_plugin_register_timeseries_fetcher(const char *name,
+		sdb_timeseries_fetcher_t *fetcher, sdb_object_t *user_data)
 {
-	return plugin_add_callback(&ts_fetcher_list, "time-series fetcher",
-			name, callback, user_data);
-} /* sdb_plugin_register_ts_fetcher */
+	return plugin_add_impl(&timeseries_fetcher_list, ts_fetcher_type, "time-series fetcher",
+			name, fetcher, user_data);
+} /* sdb_plugin_register_timeseries_fetcher */
 
 int
 sdb_plugin_register_writer(const char *name,
 		sdb_store_writer_t *writer, sdb_object_t *user_data)
 {
 	char cb_name[1024];
-	sdb_object_t *obj;
-
-	if ((! name) || (! writer))
-		return -1;
+	return plugin_add_impl(&writer_list, writer_type, "store writer",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			writer, user_data);
+} /* sdb_store_register_writer */
 
-	if (! writer_list)
-		writer_list = sdb_llist_create();
-	if (! writer_list)
-		return -1;
+int
+sdb_plugin_register_reader(const char *name,
+		sdb_store_reader_t *reader, sdb_object_t *user_data)
+{
+	char cb_name[1024];
+	return plugin_add_impl(&reader_list, reader_type, "store reader",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			reader, user_data);
+} /* sdb_plugin_register_reader */
 
-	plugin_get_name(name, cb_name, sizeof(cb_name));
+void
+sdb_plugin_unregister_all(void)
+{
+	size_t i;
 
-	obj = sdb_object_create(cb_name, sdb_plugin_writer_type,
-			writer, user_data);
-	if (! obj)
-		return -1;
+	for (i = 0; i < SDB_STATIC_ARRAY_LEN(all_lists); ++i) {
+		const char  *type =  all_lists[i].type;
+		sdb_llist_t *list = *all_lists[i].list;
 
-	if (sdb_llist_append(writer_list, obj)) {
-		sdb_object_deref(obj);
-		return -1;
-	}
+		size_t len = sdb_llist_len(list);
 
-	/* pass control to the list */
-	sdb_object_deref(obj);
+		if (! len)
+			continue;
 
-	sdb_log(SDB_LOG_INFO, "core: Registered store writer callback '%s'.",
-			cb_name);
-	return 0;
-} /* sdb_store_register_writer */
+		sdb_llist_clear(list);
+		sdb_log(SDB_LOG_INFO, "Unregistered %zu %s callback%s",
+				len, type, len == 1 ? "" : "s");
+	}
+} /* sdb_plugin_unregister_all */
 
 sdb_plugin_ctx_t
 sdb_plugin_get_ctx(void)
@@ -896,7 +1189,7 @@ sdb_plugin_get_ctx(void)
 
 	c = ctx_get();
 	if (! c) {
-		sdb_plugin_log(SDB_LOG_ERR, "core: Invalid read access to plugin "
+		sdb_log(SDB_LOG_ERR, "Invalid read access to plugin "
 				"context outside a plugin");
 		return plugin_default_ctx;
 	}
@@ -910,7 +1203,7 @@ sdb_plugin_set_ctx(sdb_plugin_ctx_t ctx, sdb_plugin_ctx_t *old)
 
 	c = ctx_get();
 	if (! c) {
-		sdb_plugin_log(SDB_LOG_ERR, "core: Invalid write access to plugin "
+		sdb_log(SDB_LOG_ERR, "Invalid write access to plugin "
 				"context outside a plugin");
 		return -1;
 	}
@@ -934,7 +1227,7 @@ sdb_plugin_current(void)
 int
 sdb_plugin_configure(const char *name, oconfig_item_t *ci)
 {
-	sdb_plugin_cb_t *plugin;
+	callback_t *plugin;
 	sdb_plugin_config_cb callback;
 
 	ctx_t *old_ctx;
@@ -944,15 +1237,15 @@ sdb_plugin_configure(const char *name, oconfig_item_t *ci)
 	if ((! name) || (! ci))
 		return -1;
 
-	plugin = SDB_PLUGIN_CB(sdb_llist_search_by_name(config_list, name));
+	plugin = CB(sdb_llist_search_by_name(config_list, name));
 	if (! plugin) {
 		ctx_t *ctx = CTX(sdb_llist_search_by_name(all_plugins, name));
 		if (! ctx)
-			sdb_log(SDB_LOG_ERR, "core: Cannot configure unknown "
-					"plugin '%s'. Missing 'LoadPlugin \"%s\"'?",
+			sdb_log(SDB_LOG_ERR, "Cannot configure unknown plugin '%s'. "
+					"Missing 'LoadPlugin \"%s\"'?",
 					name, name);
 		else
-			sdb_log(SDB_LOG_ERR, "core: Plugin '%s' did not register "
+			sdb_log(SDB_LOG_ERR, "Plugin '%s' did not register "
 					"a config callback.", name);
 		errno = ENOENT;
 		return -1;
@@ -976,11 +1269,11 @@ sdb_plugin_reconfigure_init(void)
 
 	/* deconfigure all plugins */
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_cb_t *plugin;
+		callback_t *plugin;
 		sdb_plugin_config_cb callback;
 		ctx_t *old_ctx;
 
-		plugin = SDB_PLUGIN_CB(sdb_llist_iter_get_next(iter));
+		plugin = CB(sdb_llist_iter_get_next(iter));
 		old_ctx = ctx_set(plugin->cb_ctx);
 		callback = (sdb_plugin_config_cb)plugin->cb_callback;
 		callback(NULL);
@@ -997,7 +1290,7 @@ sdb_plugin_reconfigure_init(void)
 		CTX(sdb_llist_iter_get_next(iter))->use_cnt = 0;
 	sdb_llist_iter_destroy(iter);
 
-	plugin_unregister_all();
+	sdb_plugin_unregister_all();
 	return 0;
 } /* sdb_plugin_reconfigure_init */
 
@@ -1015,7 +1308,7 @@ sdb_plugin_reconfigure_finish(void)
 		if (ctx->use_cnt)
 			continue;
 
-		sdb_log(SDB_LOG_INFO, "core: Module %s no longer in use",
+		sdb_log(SDB_LOG_INFO, "Module %s no longer in use",
 				ctx->info.plugin_name);
 		sdb_llist_iter_remove_current(iter);
 		plugin_unregister_by_name(ctx->info.plugin_name);
@@ -1033,20 +1326,20 @@ sdb_plugin_init_all(void)
 
 	iter = sdb_llist_get_iter(init_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_cb_t *cb;
+		callback_t *cb;
 		sdb_plugin_init_cb callback;
 		ctx_t *old_ctx;
 
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
-		cb = SDB_PLUGIN_CB(obj);
+		cb = CB(obj);
 
 		callback = (sdb_plugin_init_cb)cb->cb_callback;
 
 		old_ctx = ctx_set(cb->cb_ctx);
 		if (callback(cb->cb_user_data)) {
-			sdb_log(SDB_LOG_ERR, "core: Failed to initialize plugin "
-					"'%s'. Unregistering all callbacks.", obj->name);
+			sdb_log(SDB_LOG_ERR, "Failed to initialize plugin '%s'. "
+					"Unregistering all callbacks.", obj->name);
 			ctx_set(old_ctx);
 			plugin_unregister_by_name(cb->cb_ctx->info.plugin_name);
 			++ret;
@@ -1066,19 +1359,19 @@ sdb_plugin_shutdown_all(void)
 
 	iter = sdb_llist_get_iter(shutdown_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_cb_t *cb;
+		callback_t *cb;
 		sdb_plugin_shutdown_cb callback;
 		ctx_t *old_ctx;
 
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
-		cb = SDB_PLUGIN_CB(obj);
+		cb = CB(obj);
 
 		callback = (sdb_plugin_shutdown_cb)cb->cb_callback;
 
 		old_ctx = ctx_set(cb->cb_ctx);
 		if (callback(cb->cb_user_data)) {
-			sdb_log(SDB_LOG_ERR, "core: Failed to shutdown plugin '%s'.",
+			sdb_log(SDB_LOG_ERR, "Failed to shutdown plugin '%s'.",
 					obj->name);
 			++ret;
 		}
@@ -1092,7 +1385,7 @@ int
 sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 {
 	if (! collector_list) {
-		sdb_log(SDB_LOG_WARNING, "core: No collectors registered. "
+		sdb_log(SDB_LOG_WARNING, "No collectors registered. "
 				"Quiting main loop.");
 		return -1;
 	}
@@ -1110,24 +1403,24 @@ sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 		if (! obj)
 			return -1;
 
-		callback = (sdb_plugin_collector_cb)SDB_PLUGIN_CCB(obj)->ccb_callback;
+		callback = (sdb_plugin_collector_cb)CCB(obj)->ccb_callback;
 
 		if (! (now = sdb_gettime())) {
 			char errbuf[1024];
-			sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
+			sdb_log(SDB_LOG_ERR, "Failed to determine current "
 					"time in collector main loop: %s",
 					sdb_strerror(errno, errbuf, sizeof(errbuf)));
-			now = SDB_PLUGIN_CCB(obj)->ccb_next_update;
+			now = CCB(obj)->ccb_next_update;
 		}
 
-		if (now < SDB_PLUGIN_CCB(obj)->ccb_next_update) {
-			interval = SDB_PLUGIN_CCB(obj)->ccb_next_update - now;
+		if (now < CCB(obj)->ccb_next_update) {
+			interval = CCB(obj)->ccb_next_update - now;
 
 			errno = 0;
 			while (loop->do_loop && sdb_sleep(interval, &interval)) {
 				if (errno != EINTR) {
 					char errbuf[1024];
-					sdb_log(SDB_LOG_ERR, "core: Failed to sleep "
+					sdb_log(SDB_LOG_ERR, "Failed to sleep "
 							"in collector main loop: %s",
 							sdb_strerror(errno, errbuf, sizeof(errbuf)));
 					sdb_llist_insert_sorted(collector_list, obj,
@@ -1147,45 +1440,44 @@ sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 			}
 		}
 
-		old_ctx = ctx_set(SDB_PLUGIN_CCB(obj)->ccb_ctx);
-		if (callback(SDB_PLUGIN_CCB(obj)->ccb_user_data)) {
+		old_ctx = ctx_set(CCB(obj)->ccb_ctx);
+		if (callback(CCB(obj)->ccb_user_data)) {
 			/* XXX */
 		}
 		ctx_set(old_ctx);
 
-		interval = SDB_PLUGIN_CCB(obj)->ccb_interval;
+		interval = CCB(obj)->ccb_interval;
 		if (! interval)
 			interval = loop->default_interval;
 		if (! interval) {
-			sdb_log(SDB_LOG_WARNING, "core: No interval configured "
+			sdb_log(SDB_LOG_WARNING, "No interval configured "
 					"for plugin '%s'; skipping any further "
 					"iterations.", obj->name);
 			sdb_object_deref(obj);
 			continue;
 		}
 
-		SDB_PLUGIN_CCB(obj)->ccb_next_update += interval;
+		CCB(obj)->ccb_next_update += interval;
 
 		if (! (now = sdb_gettime())) {
 			char errbuf[1024];
-			sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
+			sdb_log(SDB_LOG_ERR, "Failed to determine current "
 					"time in collector main loop: %s",
 					sdb_strerror(errno, errbuf, sizeof(errbuf)));
-			now = SDB_PLUGIN_CCB(obj)->ccb_next_update;
+			now = CCB(obj)->ccb_next_update;
 		}
 
-		if (now > SDB_PLUGIN_CCB(obj)->ccb_next_update) {
-			sdb_log(SDB_LOG_WARNING, "core: Plugin '%s' took too "
+		if (now > CCB(obj)->ccb_next_update) {
+			sdb_log(SDB_LOG_WARNING, "Plugin '%s' took too "
 					"long; skipping iterations to keep up.",
 					obj->name);
-			SDB_PLUGIN_CCB(obj)->ccb_next_update = now;
+			CCB(obj)->ccb_next_update = now;
 		}
 
 		if (sdb_llist_insert_sorted(collector_list, obj,
 					plugin_cmp_next_update)) {
-			sdb_log(SDB_LOG_ERR, "core: Failed to re-insert "
-					"plugin '%s' into collector list. Unable to further "
-					"use the plugin.",
+			sdb_log(SDB_LOG_ERR, "Failed to re-insert plugin '%s' into "
+					"collector list. Unable to further use the plugin.",
 					obj->name);
 			sdb_object_deref(obj);
 			return -1;
@@ -1216,8 +1508,8 @@ sdb_plugin_cname(char *hostname)
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
 
-		callback = (sdb_plugin_cname_cb)SDB_PLUGIN_CB(obj)->cb_callback;
-		cname = callback(hostname, SDB_PLUGIN_CB(obj)->cb_user_data);
+		callback = (sdb_plugin_cname_cb)CB(obj)->cb_callback;
+		cname = callback(hostname, CB(obj)->cb_user_data);
 		if (cname) {
 			free(hostname);
 			hostname = cname;
@@ -1231,35 +1523,50 @@ sdb_plugin_cname(char *hostname)
 int
 sdb_plugin_log(int prio, const char *msg)
 {
-	sdb_llist_iter_t *iter;
+	const sdb_plugin_info_t *info;
 	int ret = -1;
 
-	bool logged = 0;
-
 	if (! msg)
 		return 0;
 
-	iter = sdb_llist_get_iter(log_list);
-	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_log_cb callback;
-		int tmp;
+	info = sdb_plugin_current();
 
-		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
-		assert(obj);
+	{
+		const char *plugin_name = info ? info->plugin_name : "";
+		char log_msg[strlen(msg) + strlen(plugin_name) + strlen(" plugin: ") + 1];
 
-		callback = (sdb_plugin_log_cb)SDB_PLUGIN_CB(obj)->cb_callback;
-		tmp = callback(prio, msg, SDB_PLUGIN_CB(obj)->cb_user_data);
-		if (tmp > ret)
-			ret = tmp;
+		sdb_llist_iter_t *iter;
+		bool logged = 0;
 
-		if (SDB_PLUGIN_CB(obj)->cb_ctx)
-			logged = 1;
-		/* else: this is an internally registered callback */
-	}
-	sdb_llist_iter_destroy(iter);
+		if (*plugin_name)
+			snprintf(log_msg, sizeof(log_msg), "%s plugin: %s",
+					plugin_name, msg);
+		else
+			strncpy(log_msg, msg, sizeof(log_msg));
+
+		iter = sdb_llist_get_iter(log_list);
+		while (sdb_llist_iter_has_next(iter)) {
+			sdb_plugin_log_cb callback;
+			int tmp;
 
-	if (! logged)
-		return fprintf(stderr, "[%s] %s\n", SDB_LOG_PRIO_TO_STRING(prio), msg);
+			sdb_object_t *obj = sdb_llist_iter_get_next(iter);
+			assert(obj);
+
+			callback = (sdb_plugin_log_cb)CB(obj)->cb_callback;
+			tmp = callback(prio, msg, CB(obj)->cb_user_data);
+			if (tmp > ret)
+				ret = tmp;
+
+			if (CB(obj)->cb_ctx)
+				logged = 1;
+			/* else: this is an internally registered callback */
+		}
+		sdb_llist_iter_destroy(iter);
+
+		if (! logged)
+			return fprintf(stderr, "[%s] %s\n",
+					SDB_LOG_PRIO_TO_STRING(prio), log_msg);
+	}
 	return ret;
 } /* sdb_plugin_log */
 
@@ -1308,8 +1615,7 @@ sdb_timeseries_t *
 sdb_plugin_fetch_timeseries(const char *type, const char *id,
 		sdb_timeseries_opts_t *opts)
 {
-	sdb_plugin_cb_t *plugin;
-	sdb_plugin_fetch_ts_cb callback;
+	ts_fetcher_t *fetcher;
 	sdb_timeseries_t *ts;
 
 	ctx_t *old_ctx;
@@ -1317,39 +1623,142 @@ sdb_plugin_fetch_timeseries(const char *type, const char *id,
 	if ((! type) || (! id) || (! opts))
 		return NULL;
 
-	plugin = SDB_PLUGIN_CB(sdb_llist_search_by_name(ts_fetcher_list, type));
-	if (! plugin) {
-		sdb_log(SDB_LOG_ERR, "core: Cannot fetch time-series of type %s: "
+	fetcher = TS_FETCHER(sdb_llist_search_by_name(timeseries_fetcher_list, type));
+	if (! fetcher) {
+		sdb_log(SDB_LOG_ERR, "Cannot fetch time-series of type %s: "
 				"no such plugin loaded", type);
 		errno = ENOENT;
 		return NULL;
 	}
 
-	old_ctx = ctx_set(plugin->cb_ctx);
-	callback = (sdb_plugin_fetch_ts_cb)plugin->cb_callback;
-	ts = callback(id, opts, plugin->cb_user_data);
+	old_ctx = ctx_set(fetcher->ts_ctx);
+	ts = fetcher->impl.fetch(id, opts, fetcher->ts_user_data);
 	ctx_set(old_ctx);
 	return ts;
 } /* sdb_plugin_fetch_timeseries */
 
+sdb_timeseries_info_t *
+sdb_plugin_describe_timeseries(const char *type, const char *id)
+{
+	ts_fetcher_t *fetcher;
+	sdb_timeseries_info_t *ts_info;
+
+	ctx_t *old_ctx;
+
+	if ((! type) || (! id))
+		return NULL;
+
+	fetcher = TS_FETCHER(sdb_llist_search_by_name(timeseries_fetcher_list, type));
+	if (! fetcher) {
+		sdb_log(SDB_LOG_ERR, "Cannot describe time-series of type %s: "
+				"no such plugin loaded", type);
+		errno = ENOENT;
+		return NULL;
+	}
+
+	old_ctx = ctx_set(fetcher->ts_ctx);
+	ts_info = fetcher->impl.describe(id, fetcher->ts_user_data);
+	ctx_set(old_ctx);
+	return ts_info;
+} /* sdb_plugin_describe_timeseries */
+
+int
+sdb_plugin_query(sdb_ast_node_t *ast,
+		sdb_store_writer_t *w, sdb_object_t *wd,
+		sdb_query_opts_t *opts, sdb_strbuf_t *errbuf)
+{
+	query_writer_t qw = QUERY_WRITER_INIT(w, wd);
+	reader_t *reader;
+	sdb_object_t *q;
+
+	size_t n = sdb_llist_len(reader_list);
+	int status = 0;
+
+	if (! ast)
+		return 0;
+
+	if (opts)
+		qw.opts = *opts;
+
+	if ((ast->type != SDB_AST_TYPE_FETCH)
+			&& (ast->type != SDB_AST_TYPE_LIST)
+			&& (ast->type != SDB_AST_TYPE_LOOKUP)) {
+		sdb_log(SDB_LOG_ERR, "Cannot execute query of type %s",
+				SDB_AST_TYPE_TO_STRING(ast));
+		sdb_strbuf_sprintf(errbuf, "Cannot execute query of type %s",
+				SDB_AST_TYPE_TO_STRING(ast));
+		return -1;
+	}
+
+	if (n != 1) {
+		char *msg = (n > 0)
+			? "Cannot execute query: multiple readers not supported"
+			: "Cannot execute query: no readers registered";
+		sdb_strbuf_sprintf(errbuf, "%s", msg);
+		sdb_log(SDB_LOG_ERR, "%s", msg);
+		return -1;
+	}
+
+	reader = READER(sdb_llist_get(reader_list, 0));
+	assert(reader);
+
+	q = reader->impl.prepare_query(ast, errbuf, reader->r_user_data);
+	if (q)
+		status = reader->impl.execute_query(q, &query_writer, SDB_OBJ(&qw),
+				errbuf, reader->r_user_data);
+	else
+		status = -1;
+
+	sdb_object_deref(SDB_OBJ(q));
+	sdb_object_deref(SDB_OBJ(reader));
+	return status;
+} /* sdb_plugin_query */
+
 int
 sdb_plugin_store_host(const char *name, sdb_time_t last_update)
 {
+	sdb_store_host_t host = SDB_STORE_HOST_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
 	int status = 0;
 
 	if (! name)
 		return -1;
 
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store host: no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(name));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	host.name = cname;
+	host.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_HOST, NULL, -1, NULL, cname,
+				host.last_update, &host.interval)) {
+		free(cname);
+		return 1;
+	}
+	host.backends = (const char * const *)backends;
+	get_backend(backends, &host.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_host(name, last_update, writer->user_data))
-			status = -1;
+		s = writer->impl.store_host(&host, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+	free(cname);
 	return status;
 } /* sdb_plugin_store_host */
 
@@ -1357,22 +1766,62 @@ int
 sdb_plugin_store_service(const char *hostname, const char *name,
 		sdb_time_t last_update)
 {
+	sdb_store_service_t service = SDB_STORE_SERVICE_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
+	sdb_data_t d;
+
 	int status = 0;
 
 	if ((! hostname) || (! name))
 		return -1;
 
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store service: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	service.hostname = cname;
+	service.name = name;
+	service.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_SERVICE, cname, -1, NULL, name,
+				service.last_update, &service.interval)) {
+		free(cname);
+		return 1;
+	}
+	service.backends = (const char * const *)backends;
+	get_backend(backends, &service.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_service(hostname, name, last_update,
-					writer->user_data))
-			status = -1;
+		s = writer->impl.store_service(&service, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+
+	if (! status) {
+		/* record the hostname as an attribute */
+		d.type = SDB_TYPE_STRING;
+		d.data.string = cname;
+		if (sdb_plugin_store_service_attribute(cname, name,
+					"hostname", &d, service.last_update))
+			status = -1;
+	}
+
+	free(cname);
 	return status;
 } /* sdb_plugin_store_service */
 
@@ -1380,25 +1829,70 @@ int
 sdb_plugin_store_metric(const char *hostname, const char *name,
 		sdb_metric_store_t *store, sdb_time_t last_update)
 {
+	sdb_store_metric_t metric = SDB_STORE_METRIC_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
+	sdb_data_t d;
+
 	int status = 0;
 
 	if ((! hostname) || (! name))
 		return -1;
 
-	if ((! store->type) || (! store->id))
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store metric: no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	if (store && ((! store->type) || (! store->id)))
 		store = NULL;
 
+	metric.hostname = cname;
+	metric.name = name;
+	if (store) {
+		if (store->last_update < last_update)
+			store->last_update = last_update;
+		metric.stores = store;
+		metric.stores_num = 1;
+	}
+	metric.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_METRIC, cname, -1, NULL, name,
+				metric.last_update, &metric.interval)) {
+		free(cname);
+		return 1;
+	}
+	metric.backends = (const char * const *)backends;
+	get_backend(backends, &metric.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_metric(hostname, name, store, last_update,
-					writer->user_data))
-			status = -1;
+		s = writer->impl.store_metric(&metric, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+
+	if (! status) {
+		/* record the hostname as an attribute */
+		d.type = SDB_TYPE_STRING;
+		d.data.string = cname;
+		if (sdb_plugin_store_metric_attribute(cname, name,
+					"hostname", &d, metric.last_update))
+			status = -1;
+	}
+
+	free(cname);
 	return status;
 } /* sdb_plugin_store_metric */
 
@@ -1406,22 +1900,51 @@ int
 sdb_plugin_store_attribute(const char *hostname, const char *key,
 		const sdb_data_t *value, sdb_time_t last_update)
 {
+	sdb_store_attribute_t attr = SDB_STORE_ATTRIBUTE_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
 	int status = 0;
 
 	if ((! hostname) || (! key) || (! value))
 		return -1;
 
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store attribute: no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	attr.parent_type = SDB_HOST;
+	attr.parent = cname;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_ATTRIBUTE, cname, -1, NULL, key,
+				attr.last_update, &attr.interval)) {
+		free(cname);
+		return 1;
+	}
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_attribute(hostname, key, value, last_update,
-					writer->user_data))
-			status = -1;
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+	free(cname);
 	return status;
 } /* sdb_plugin_store_attribute */
 
@@ -1429,22 +1952,53 @@ int
 sdb_plugin_store_service_attribute(const char *hostname, const char *service,
 		const char *key, const sdb_data_t *value, sdb_time_t last_update)
 {
+	sdb_store_attribute_t attr = SDB_STORE_ATTRIBUTE_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
 	int status = 0;
 
 	if ((! hostname) || (! service) || (! key) || (! value))
 		return -1;
 
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store service attribute: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	attr.hostname = cname;
+	attr.parent_type = SDB_SERVICE;
+	attr.parent = service;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_ATTRIBUTE, cname, SDB_SERVICE, service, key,
+				attr.last_update, &attr.interval)) {
+		free(cname);
+		return 1;
+	}
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_service_attr(hostname, service,
-					key, value, last_update, writer->user_data))
-			status = -1;
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+	free(cname);
 	return status;
 } /* sdb_plugin_store_service_attribute */
 
@@ -1452,22 +2006,53 @@ int
 sdb_plugin_store_metric_attribute(const char *hostname, const char *metric,
 		const char *key, const sdb_data_t *value, sdb_time_t last_update)
 {
+	sdb_store_attribute_t attr = SDB_STORE_ATTRIBUTE_INIT;
+	char *backends[1];
+	char *cname;
+
 	sdb_llist_iter_t *iter;
 	int status = 0;
 
 	if ((! hostname) || (! metric) || (! key) || (! value))
 		return -1;
 
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "Cannot store metric attribute: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "strdup failed");
+		return -1;
+	}
+
+	attr.hostname = cname;
+	attr.parent_type = SDB_METRIC;
+	attr.parent = metric;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update ? last_update : sdb_gettime();
+	if (get_interval(SDB_ATTRIBUTE, cname, SDB_METRIC, metric, key,
+				attr.last_update, &attr.interval)) {
+		free(cname);
+		return 1;
+	}
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
 	iter = sdb_llist_get_iter(writer_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_writer_t *writer;
-		writer = SDB_PLUGIN_WRITER(sdb_llist_iter_get_next(iter));
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
 		assert(writer);
-		if (writer->impl.store_metric_attr(hostname, metric,
-					key, value, last_update, writer->user_data))
-			status = -1;
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
 	}
 	sdb_llist_iter_destroy(iter);
+	free(cname);
 	return status;
 } /* sdb_plugin_store_metric_attribute */