Anatomy of an Append Operation

Now we can look at how GFS handles an append operation.

A record append is what sets GFS apart from other distributed file systems. In an ordinary write, the client picks the offset where its data goes. When two clients write to the same region at the same time, the writes can race. The region can hold fragments from both of them, mixed together.

A record append avoids that. The client sends only the data, with no offset. GFS picks the offset, appends the data there, and hands that offset back to the client. The guarantee behind this is at-least-once