Downgrade from postgres 9.5 dependency by not using 'on conflict do n…

…othing' (askmike#1478)

* Downgrade from postgres 9.5 dependency by not using 'on conflict do nothing'

docs/commandline/tradebot.md

@@ -6,11 +6,11 @@ You can set Gekko up as a tradebot, this will instruct Gekko to:
 - Run a strategy (in semi-realtime) over live market data.
 - Automatically create buy/sell orders based on signals coming from the strategy.
 
-*As with everything in Gekko, the tradebot will make decisions based on the by YOU selected/configured/created strategy. If you end up losing money you have no one to blame but yourself.*
+*As with everything in Gekko, the tradebot will make decisions based on the strategy selected/configured/created **by YOU**. If you end up losing money, you have no one to blame but yourself.*
 
 ## Configuration
 
-First set up Gekko for commandline usage (see [this document](./about_the_commandline.md) for details). After that configure the following plugins:
+First, set up Gekko for commandline usage (see [this document](./about_the_commandline.md) for details). After that, configure the following plugins:
 
 - `config.watch` - the market to trade on.
 - `candleWriter` - (optional) also store market data to disk.
@@ -19,4 +19,4 @@ First set up Gekko for commandline usage (see [this document](./about_the_comman
 
 Turn off the paperTrader (to not get conflicting profit reports).
 
-Once done run Gekko in live mode.
+Once done, run Gekko in live mode.

plugins/postgresql/writer.js

@@ -45,7 +45,8 @@ Store.prototype.writeCandles = function() {
   var stmt = `
   INSERT INTO ${postgresUtil.table('candles')}
   (start, open, high,low, close, vwp, volume, trades)
-  values($1, $2, $3, $4, $5, $6, $7, $8) ON CONFLICT DO NOTHING;
+  select $1, $2, $3, $4, $5, $6, $7, $8
+  WHERE NOT EXISTS (select id from ${postgresUtil.table('candles')} where start=$1);
   `;
 
   _.each(this.cache, candle => {