Commit f428d5070f3dc01fb29d716b2c4fdf1722204de6
readme
Dominic Tarr committed on 11/29/2016, 2:10:55 PMParent: 2c2005a0ab6c3b6a9d80225999d269debe9a0ec5
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| 2 | 2 … | ||
| 3 | 3 … | A flumeview into a reduce function. | |
| 4 | 4 … | Stream append-only log data into a reduce function to calculate a state. | |
| 5 | 5 … | ||
| 6 … | +## Example | ||
| 7 … | + | ||
| 8 … | +``` js | ||
| 9 … | +var FlumeLog = require('flumelog-offset') | ||
| 10 … | +var codec = require('flumecodec') | ||
| 11 … | +var Flume = require('flumedb') | ||
| 12 … | +var Reduce = require('flumeview-reduce') | ||
| 13 … | + | ||
| 14 … | +//statistics exports a reduce function that calculates | ||
| 15 … | +//mean, stdev, etc! | ||
| 16 … | +var statistics = require('statistics') | ||
| 17 … | + | ||
| 18 … | +//initialize a flumelog with a codec. | ||
| 19 … | +//this example uses flumelog-offset, but any flumelog is valid. | ||
| 20 … | +var log = FlumeLog(file, 1024*16, codec.json) //use any flume log | ||
| 21 … | + | ||
| 22 … | +//attach the reduce function. | ||
| 23 … | +var db = Flume(log).use('stats', | ||
| 24 … | + Reduce(1, statistics, function (data) { | ||
| 25 … | + return data.value | ||
| 26 … | + }) | ||
| 27 … | + | ||
| 28 … | +db.append({value: 1}, function (err) { | ||
| 29 … | + | ||
| 30 … | + db.stats.get(function (err, stats) { | ||
| 31 … | + console.log(stats) // => {mean: 1, stdev: 0, count: 1, sum: 1, ...} | ||
| 32 … | + }) | ||
| 33 … | +}) | ||
| 34 … | +``` | ||
| 35 … | + | ||
| 36 … | +## FlumeViewReduce(version, reduce, map?) => FlumeView | ||
| 37 … | + | ||
| 38 … | +construct a flumeview from this reduce function. `version` should be a number, | ||
| 39 … | +and must be provided. If you make a breaking change to either `reduce` or `map` | ||
| 40 … | +then increment `version` and the view will be rebuilt. | ||
| 41 … | + | ||
| 42 … | +`map` is optional. If map is applied, then each item in the log is passed to `map` | ||
| 43 … | +and then if the returned value is not null, it is passed to reduce. | ||
| 44 … | + | ||
| 45 … | +``` js | ||
| 46 … | +var _data = map(data) | ||
| 47 … | +if(_data != null) | ||
| 48 … | + state = reduce(state, map(data)) | ||
| 49 … | +``` | ||
| 50 … | + | ||
| 51 … | +using a `map` function is useful, because it enables efficiently streaming the realtime | ||
| 52 … | +changes in the state to a remote client. | ||
| 53 … | + | ||
| 54 … | +then, pass the flumeview to `db.use(name, flumeview)` | ||
| 55 … | +and you'll have access to the flumeview methods on `db[name]...` | ||
| 56 … | + | ||
| 57 … | +## db[name].get(cb) | ||
| 58 … | + | ||
| 59 … | +get the current state of the reduce. This will wait until the view is up to date, if necessary. | ||
| 60 … | + | ||
| 61 … | +## db[name].stream({live: boolean}) => PullSource | ||
| 62 … | + | ||
| 63 … | +Stream the changing reduce state. for this to work, a map function must be provided. | ||
| 64 … | + | ||
| 65 … | +If so, the same reduce function can be used to process the output. | ||
| 66 … | + | ||
| 6 | 67 … | ## License | |
| 7 | 68 … | ||
| 8 | 69 … | MIT | |
| 9 | 70 … | ||
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