Manually forcing a merge

Manually forcing a merge is considered a one-time option, because after the merge operation is performed (via a temporary aggressive change to the merge policy), the merge policy reverts to its previous setting.

Forcing an index merge is used to perform a complete merge of all generations without making a change to the default merge policy. When you issue this command, it is routed to the leader Dgraph node and the Dgraph starts a manual merge of its index files. After the merging is performed, the merge policy reverts to its previous setting.

Forcing a merge implies starting a full merge of all generations of index files. When running this command, be aware of the following considerations:

Memory requirements. Forcing a complete merge utilizes the server's memory. If the amount of memory reaches the amount of RAM that is available, the merge operation will continue to work, but could run substantially slower and have a higher impact on query performance.
Disk space requirements. Forcing a merge requires provisioning two times the amount of disk space as the current size of the index files. However, if the Dgraph is performing other tasks (such as updates), the merge may require disk space that is three times the size of the index files. If not enough disk space is provisioned, it could be disruptive to force a complete merge. This consideration is especially important for running this command on the Dgraph in a production environment.