Quote from: tagada on May 11, 2013, 09:33:19 AM

Quote from: TobbeLino on May 10, 2013, 09:53:30 PM

Yes, the bot uses the "since"-parameter, and it will make one fetch for each sample interval back in time to calculate EMA. Total 144 calls when starting the bot or changing sample interval (EMA-values need to be recalculated). This many calls may be a problem in itself since I think MtGox's (or Couldflare's) DDoS-protection might kick in and block your IP when making so many calls in a short time.

But the problem with API v1 and v2 is that it seems that the size of the chunks has been increased from 100 to 1000.

For instance: https://data.mtgox.com/api/2/BTCUSD/money/trades/fetch?since=1354250571691361 will return 1000 trades
And: https://data.mtgox.com/api/0/data/getTrades.php?Currency=USD&since=1354250571691361 will return 100.

I've taken a quick look at the code, and a few things come to mind. First, that 144 is pretty arbitrary: since EMA is a recursive calculation, its accuracy is very dependent on the number of samples. After a certain point it becomes less relevant since the further you go back, the less the weight given to the data, but 200 * whatever timeframe you're trading is a generally accepted sample size. I remember someone complaining that the initial sample size was not accurate enough so Piotr increased it to 144 which should be an ok compromise, but it won't hurt if you have more.

So you could either keep making these 144 requests of 1000 trades and then divide that by your trading sample size, which would give you about 10 times more candles to back your calculations on, or you can make that 144 dynamic by making requests with a timestamp equal to (number of samples required for accuracy x trading sample size) instead of this fixed 144. In other words, fetch only as much as you need according to your sample size instead of making an arbitrary number of requests. This fixed value made sense when the original bot only dealt with H1 trading and needed 144H of backdata, but not so much now that you allow users to define the trading candle size.

Also, this history and its subsequent updated candles should probably be cached into localstorage until next launch. Since for a 60m candle you're fetching about 5 days worth of history, chances are that some of that data will still be valid on next bot launch, and that would also prevent from refetching everything upon a simple change of parameters.

Yes, 144 is from the original bot, and I have not dared to change or question it

However, I think the number of samples should be the same no matter what the sample interval is (the bot fetches 144 samples, not 144 hours of samples). The EMA-vaules are calculated from the samples - independent of the interval, so the accuracy should be exactly the same as the original bot for any sample interval.

Caching samples would probably be a good idea!
Because calling the MtGox API repeatedly in a short time could mabe get you blocked by their DDoS-protection...