Maintaining NeoWiki

Upkeep tasks for an evaluation NeoWiki instance. For first-time setup, see installation.

Rebuilding the graph

NeoWiki stores its canonical data in MediaWiki revision slots and keeps a regenerable copy in each configured backend — Neo4j and any SPARQL store — for querying. You can wipe and rebuild that copy from the canonical slots at any time. From the MediaWiki root:

php maintenance/run.php NeoWiki:RebuildGraphDatabases

It re-saves every Subject from each page's latest revision into every backend, and removes the pages MediaWiki no longer has. Run it to:

• Recover after a backend wipe or restore.
• Fix any drift between a backend's copy and the canonical revision slots.

Two things to plan around:

• It reconciles pages, not stray data. Anything the projection never knew about — a node written directly to Neo4j, say, or a named graph left behind in a SPARQL store — is not something the rebuild can find. For a guaranteed-clean result, empty the backend before rebuilding: wipe Neo4j's data volume, or drop the wiki's named graphs from the store.
• It runs as a single sequential process with no batching or resume, so the time scales with the number of pages. Plan downtime on large wikis.

Upgrades

Update the NeoWiki code, then run MediaWiki's standard updater from the root:

php maintenance/run.php update --quick

If the new version changes how data is stored in the graph, rebuild the projection afterwards.

NeoWiki is pre-release, so a new version can change the canonical revision-slot format with no migration path. Your evaluation data may not survive an upgrade, so be ready to recreate it from scratch — a projection rebuild does not recover data the new version can no longer read.

What happens during a Neo4j outage

• Editing pages works. Edits, deletions and undeletions all commit. NeoWiki logs the projection failure on the NeoWiki channel.
• Editing and displaying Subjects fails, along with queries and anything else that reads the graph.

Once Neo4j is back, rebuild the graph: it repairs both a failed save and a failed delete. It names any page it could not reconcile; re-run it once you have cleared the cause.

Route the NeoWiki log channel somewhere you read. On a default MediaWiki install it goes nowhere, which leaves the rebuild's output as your only sign that anything went wrong.

Backups

Back up the MediaWiki database as usual; it holds the canonical data. Neo4j and any SPARQL store need no backup — they are regenerable copies you can rebuild from the revision slots.