Core: change default xlog size from 200 MB to 512 MB

Closes #9341

Author: mikemccand

docs/reference/index-modules/translog.asciidoc

@@ -13,7 +13,7 @@ After how many operations to flush. Defaults to `unlimited`.
 
 `index.translog.flush_threshold_size`:: 
 
-Once the translog hits this size, a flush will happen. Defaults to `200mb`.
+Once the translog hits this size, a flush will happen. Defaults to `512mb`.
 
 `index.translog.flush_threshold_period`:: 
 

src/main/java/org/elasticsearch/index/translog/TranslogService.java

@@ -81,7 +81,7 @@ public TranslogService(ShardId shardId, @IndexSettings Settings indexSettings, I
         this.indexShard = indexShard;
         this.translog = translog;
         this.flushThresholdOperations = componentSettings.getAsInt(FLUSH_THRESHOLD_OPS_KEY, componentSettings.getAsInt("flush_threshold", Integer.MAX_VALUE));
-        this.flushThresholdSize = componentSettings.getAsBytesSize(FLUSH_THRESHOLD_SIZE_KEY, new ByteSizeValue(200, ByteSizeUnit.MB));
+        this.flushThresholdSize = componentSettings.getAsBytesSize(FLUSH_THRESHOLD_SIZE_KEY, new ByteSizeValue(512, ByteSizeUnit.MB));
         this.flushThresholdPeriod = componentSettings.getAsTime(FLUSH_THRESHOLD_PERIOD_KEY, TimeValue.timeValueMinutes(30));
         this.interval = componentSettings.getAsTime(FLUSH_THRESHOLD_INTERVAL_KEY, timeValueMillis(5000));
         this.disableFlush = componentSettings.getAsBoolean(FLUSH_THRESHOLD_DISABLE_FLUSH_KEY, false);