Increase cache-snapshot-memory-size default

With the recent changes to compactions and snapshotting, the current
default can create lots of small level 1 TSM files.  This increases
the default in order to create larger level 1 files and less disk
utilization.

etc/config.sample.toml

@@ -79,7 +79,7 @@
   # snapshot the cache and write it to a TSM file, freeing up memory
   # Valid size suffixes are k, m, or g (case insensitive, 1024 = 1k).
   # Values without a size suffix are in bytes.
-  # cache-snapshot-memory-size = "25m"
+  # cache-snapshot-memory-size = "256m"
 
   # CacheSnapshotWriteColdDuration is the length of time at
   # which the engine will snapshot the cache and write it to

tsdb/config.go

@@ -26,7 +26,7 @@ const (
 
 	// DefaultCacheSnapshotMemorySize is the size at which the engine will
 	// snapshot the cache and write it to a TSM file, freeing up memory
-	DefaultCacheSnapshotMemorySize = 25 * 1024 * 1024 // 25MB
+	DefaultCacheSnapshotMemorySize = 256 * 1024 * 1024 // 256MB
 
 	// DefaultCacheSnapshotWriteColdDuration is the length of time at which
 	// the engine will snapshot the cache and write it to a new TSM file if