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comparison mod_storage_multi/mod_storage_multi.lua @ 1492:8c4a2d85e8bf

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mod_storage_multi: Multi-backend storage module (WIP)
author Kim Alvefur <zash@zash.se>
date Thu, 21 Aug 2014 23:14:55 +0200
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1491:e7294423512f 1492:8c4a2d85e8bf
1 -- mod_storage_multi
2
3 local storagemanager = require"core.storagemanager";
4 local backends = module:get_option_array(module.name); -- TODO better name?
5
6 -- TODO migrate data "upwards"
7
8 -- one → one successful write is success
9 -- all → all backends must report success
10 -- majority → majority of backends must report success
11 local policy = module:get_option_string(module.name.."_policy", "all");
12
13 local keyval_store = {};
14 keyval_store.__index = keyval_store;
15
16 function keyval_store:get(username)
17 local backends = self.backends;
18 local data, err;
19 for i = 1, #backends do
20 module:log("debug", "%s:%s:get(%q)", tostring(backends[i].get), backends[i]._store, username);
21 data, err = backends[i]:get(username);
22 if err then
23 module:log("error", tostring(err));
24 elseif not data then
25 module:log("debug", "No data returned");
26 else
27 module:log("debug", "Data returned");
28 return data, err;
29 end
30 end
31 end
32
33 -- This is where it gets complicated
34 function keyval_store:set(username, data)
35 local backends = self.backends;
36 local ok, err, backend;
37 local all, one, oks = true, false, 0;
38 for i = 1, #backends do
39 backend = backends[i];
40 module:log("debug", "%s:%s:set(%q)", tostring(backends[i].get), backends[i].store, username);
41 ok, err = backend:set(username, data);
42 if not ok then
43 module:log("error", "Error in storage driver %s: %s", backend.name, tostring(err));
44 else
45 oks = oks + 1;
46 end
47 one = one or ok; -- At least one successful write
48 all = all and ok; -- All successful
49 end
50 if policy == "all" then
51 return all, err
52 elseif policy == "majority" then
53 return oks > (#backends/2), err;
54 end
55 -- elseif policy == "one" then
56 return one, err;
57 end
58
59 local stores = {
60 keyval = keyval_store;
61 }
62
63 local driver = {};
64
65 function driver:open(store, typ)
66 local store_mt = stores[typ or "keyval"];
67 if store_mt then
68 local my_backends = {};
69 local driver, opened
70 for i = 1, #backends do
71 driver = storagemanager.load_driver(module.host, backends[i]);
72 opened = driver:open(store, typ);
73 my_backends[i] = assert(driver:open(store, typ));
74 my_backends[i]._store = store;
75 end
76 return setmetatable({ backends = my_backends }, store_mt);
77 end
78 return nil, "unsupported-store";
79 end
80
81 module:provides("storage", driver);