Snapshot Move

In this video, we demonstrate how Dgraph automatically syncs a restated alpha.

We begin by executing the following steps:

  • Start zero with replica count set to 3
  • Start 3 Alphas (alpha1, alpha2, alpha3). The third alpha is given a flag --vmodule=server=3, allowing for better query logging
  • The Dgraph increment tool is used to introduce a new predicate counter.val. This is an integer which is incremented.
  • We review the state of the cluster and predicates in Ratel. The three alphas belong to one group, implying that each Alpha is a replica of the data.

We do the following steps to demonstrate that a restarted alpha will receive snapshots

  • Alpha3 is stopped
  • The Dgraph increment tool is run several times to ensure that the counter.val drifts from the last value available with alpha3.
  • Start alpha3
  • The Dgraph tool is again run, but this time directly against alpha3. It is noted that alpha3 has already received the snapshot and records the correct incremented value of counter.val
  • The logs from alpha3 show that it received an increment mutation