mod_storage_multi: Multi-backend storage module (WIP)

Thu, 21 Aug 2014 23:14:55 +0200

author
Kim Alvefur <zash@zash.se>
date
Thu, 21 Aug 2014 23:14:55 +0200
changeset 1492
8c4a2d85e8bf
parent 1491
e7294423512f
child 1493
d5e8758d391d

mod_storage_multi: Multi-backend storage module (WIP)

mod_storage_multi/mod_storage_multi.lua file | annotate | diff | comparison | revisions
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_storage_multi/mod_storage_multi.lua	Thu Aug 21 23:14:55 2014 +0200
@@ -0,0 +1,81 @@
+-- mod_storage_multi
+
+local storagemanager = require"core.storagemanager";
+local backends = module:get_option_array(module.name); -- TODO better name?
+
+-- TODO migrate data "upwards"
+
+-- one → one successful write is success
+-- all → all backends must report success
+-- majority → majority of backends must report success
+local policy = module:get_option_string(module.name.."_policy", "all");
+
+local keyval_store = {};
+keyval_store.__index = keyval_store;
+
+function keyval_store:get(username)
+	local backends = self.backends;
+	local data, err;
+	for i = 1, #backends do
+		module:log("debug", "%s:%s:get(%q)", tostring(backends[i].get), backends[i]._store, username);
+		data, err = backends[i]:get(username);
+		if err then
+			module:log("error", tostring(err));
+		elseif not data then
+			module:log("debug", "No data returned");
+		else
+			module:log("debug", "Data returned");
+			return data, err;
+		end
+	end
+end
+
+-- This is where it gets complicated
+function keyval_store:set(username, data)
+	local backends = self.backends;
+	local ok, err, backend;
+	local all, one, oks = true, false, 0;
+	for i = 1, #backends do
+		backend = backends[i];
+		module:log("debug", "%s:%s:set(%q)", tostring(backends[i].get), backends[i].store, username);
+		ok, err = backend:set(username, data);
+		if not ok then
+			module:log("error", "Error in storage driver %s: %s", backend.name, tostring(err));
+		else
+			oks = oks + 1;
+		end
+		one = one or ok; -- At least one successful write
+		all = all and ok; -- All successful
+	end
+	if policy == "all" then
+		return all, err
+	elseif policy == "majority" then
+		return oks > (#backends/2), err;
+	end
+	-- elseif policy == "one" then
+	return one, err;
+end
+
+local stores = {
+	keyval = keyval_store;
+}
+
+local driver = {};
+
+function driver:open(store, typ)
+	local store_mt = stores[typ or "keyval"];
+	if store_mt then
+		local my_backends = {};
+		local driver, opened
+		for i = 1, #backends do
+			 driver = storagemanager.load_driver(module.host, backends[i]);
+			 opened = driver:open(store, typ);
+			 my_backends[i] = assert(driver:open(store, typ));
+			 my_backends[i]._store = store;
+		end
+		return setmetatable({ backends = my_backends }, store_mt);
+	end
+	return nil, "unsupported-store";
+end
+
+module:provides("storage", driver);

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