GC: Consider size of value while rewriting (dgraph-io#1357) (dgraph-i…

…o#1505)

The existing code doesn't consider the size of the value while
calculating the size of the entry batch in rewrite method.
This PR fixes it.

Fixes dgraph-io#1292

(cherry picked from commit 14386ac)

Co-authored-by: Ibrahim Jarif <ibrahim@dgraph.io>

value.go

@@ -411,6 +411,11 @@ func (vlog *valueLog) rewrite(f *logFile, tr trace.Trace) error {
 
 			ne.Value = append([]byte{}, e.Value...)
 			es := int64(ne.estimateSize(vlog.opt.ValueThreshold))
+			// Consider size of value as well while considering the total size
+			// of the batch. There have been reports of high memory usage in
+			// rewrite because we don't consider the value size. See #1292.
+			es += int64(len(e.Value))
+
 			// Ensure length and size of wb is within transaction limits.
 			if int64(len(wb)+1) >= vlog.opt.maxBatchCount ||
 				size+es >= vlog.opt.maxBatchSize {