Gremlin query hints for using the results cache - Amazon Neptune
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Gremlin query hints for using the results cache

The following query hints can be used when the query results cache is enabled.

Gremlin enableResultCache query hint

The enableResultCache query hint with a value of true causes query results to be returned from the cache if they have already been cached. If not, it returns new results and caches them until such time as they are cleared from the cache. For example:

g.with('Neptune#enableResultCache', true) .V().has('genre','drama').in('likes')

Later, you can access the cached results by issuing exactly the same query again.

If the value of this query hint is false, or if it isn't present, query results are not cached. However, setting it to false does not clear existing cached results. To clear cached results, use the invalidateResultCache or invalidateResultCachekey hint.

Gremlin enableResultCacheWithTTL query hint

The enableResultCacheWithTTL query hint also returns cached results if there are any, without affecting the TTL of results already in the cache. If there are currently no cached results, the query returns new results and caches them for the time to live (TTL) specified by the enableResultCacheWithTTL query hint. That time to live is specified in seconds. For example, the following query specifies a time to live of sixty seconds:

g.with('Neptune#enableResultCacheWithTTL', 60) .V().has('genre','drama').in('likes')

Before the 60-second time-to-live is over, you can use the same query (here, g.V().has('genre','drama').in('likes')) with either the enableResultCache or the enableResultCacheWithTTL query hint to access the cached results.

Note

The time to live specified with enableResultCacheWithTTL does not affect results that have already been cached.

  • If results were previously cached using enableResultCache, the cache must first be explicitly cleared before enableResultCacheWithTTL generates new results and caches them for the TTL that it specifies.

  • If results were previously cached using enableResultCachewithTTL, that previous TTL must first expire before enableResultCacheWithTTL generates new results and caches them for the TTL that it specifies.

After the time to live has passed, the cached results for the query are cleared, and a subsequent instance of the same query then returns new results. If enableResultCacheWithTTL is attached to that subsequent query, the new results are cached with the TTL that it specifies.

Gremlin invalidateResultCacheKey query hint

The invalidateResultCacheKey query hint can take a true or false value. A true value causes cached results for the the query to which invalidateResultCacheKey is attached to be cleared. For example, the following example causes results cached for the query key g.V().has('genre','drama').in('likes') to be cleared:

g.with('Neptune#invalidateResultCacheKey', true) .V().has('genre','drama').in('likes')

The example query above does not cause its new results to be cached. You can include enableResultCache (or enableResultCacheWithTTL) in the same query if you want to cache the new results after clearing the existing cached ones:

g.with('Neptune#enableResultCache', true) .with('Neptune#invalidateResultCacheKey', true) .V().has('genre','drama').in('likes')

Gremlin invalidateResultCache query hint

The invalidateResultCache query hint can take a true or false value. A true value causes all results in the results cache to be cleared. For example:

g.with('Neptune#invalidateResultCache', true) .V().has('genre','drama').in('likes')

The example query above does not cause its results to be cached. You can include enableResultCache (or enableResultCacheWithTTL) in the same query if you want to cache new results after completely clearing the existing cache:

g.with('Neptune#enableResultCache', true) .with('Neptune#invalidateResultCache', true) .V().has('genre','drama').in('likes')

Gremlin numResultsCached query hint

The numResultsCached query hint can only be used with queries that contain iterate(), and it specifies the maximum number of results to cache for the query to which it is attached. Note that the results cached when numResultsCached is present are not returned, only cached.

For example, the following query specifies that up to 100 of its results should be cached, but none of those cached results returned:

g.with('Neptune#enableResultCache', true) .with('Neptune#numResultsCached', 100) .V().has('genre','drama').in('likes').iterate()

You can then use a query like the following to retrieve a range of the cached results (here, the first ten):

g.with('Neptune#enableResultCache', true) .with('Neptune#numResultsCached', 100) .V().has('genre','drama').in('likes').range(0, 10)

Gremlin noCacheExceptions query hint

The noCacheExceptions query hint can take a true or false value. A true value causes any exceptions related to the results cache to be suppressed. For example:

g.with('Neptune#enableResultCache', true) .with('Neptune#noCacheExceptions', true) .V().has('genre','drama').in('likes')

In particular, this suppresses the QueryLimitExceededException, which is raised if the results of a query are too large to fit in the results cache.