Caching

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When remote documents are fetched over HTTP, Comunica engine uses HTTP-dependent intermediary caches (e.g. in-memory triple indexes, JSON-LD contexts) to optimize future reuse. These intermediary caches are aware of HTTP caching semantics (e.g. RFC 7234/9111), so that these caches can be reused across query executions if the cached value is still valid.

Within the scope of a single query execution, HTTP responses are always assumed to be cacheable, even if no caching headers were defined for them.

Cache invalidation

If you forcefully want to invalidate the cache within your application, you can do this as follows:

// Invalidate the full cache
await myEngine.invalidateHttpCache();

// Invalidate a single document
await myEngine.invalidateHttpCache('http://example.org/page.html');

Optionally, you can also pass the noCache: true flag to your context to invalidate the cache before query execution starts:

const bindingsStream = await myEngine.queryBindings(`SELECT * WHERE { ?s ?p ?o }`, {
  sources: ['http://xmlns.com/foaf/spec/20140114.rdf'],
  noCache: true,
});

HTTP-level caching

By default, Comunica only uses intermediary caches such as triple indexes, but it does not cache actual HTTP responses. This in-memory HTTP cache can be enabled separately as follows:

const bindingsStream = await myEngine.queryBindings(`CONSTRUCT WHERE { ?s1 ?p1 ?o1. ?s2 ?p2 ?o2 }`, {
  sources: ['https://fragments.dbpedia.org/2015/en'],
  httpCache: true,
});