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We’re overhauling Dgraph’s docs to make them clearer and more approachable. If you notice any issues during this transition or have suggestions, please let us know.
Dgraph supports Persistent Queries. When a client uses persistent queries, the client only sends the hash of a query to the server. The server has a list of known hashes and uses the associated query accordingly. Persistent queries significantly improve the performance and the security of an app since the smaller hash signature reduces bandwidth utilization and speeds up client loading times.

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Persisted query logic

The execution of Persistent Queries follows this logic:
  • If the extensions key isn’t provided in the GET request, Dgraph processes the request as usual
  • If a persistedQuery exists under the extensions key, Dgraph tries to process a Persisted Query:
    • if no sha256 hash is provided, process the query without persisting
    • if the sha256 hash is provided, try to retrieve the persisted query
Example: 
{
  "persistedQuery": {
    "sha256Hash": "b952c19b894e1aa89dc05b7d53e15ab34ee0b3a3f11cdf3486acef4f0fe85c52"
  }
}

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Create

To create a Persistent Query, both query and sha256 must be provided. Dgraph verifies the hash and performs a lookup. If the query doesn’t exist, Dgraph stores the query, provided that the sha256 of the query is correct. Finally, Dgraph processes the query and returns the results. Example: 
curl -g 'http://localhost:8080/graphql/?query={sample_query}&extensions={"persistedQuery":{"sha256Hash":"b952c19b894e1aa89dc05b7d53e15ab34ee0b3a3f11cdf3486acef4f0fe85c52"}}'

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Lookup

If only a sha256 is provided, Dgraph does a look-up, and processes the query if found. Otherwise a PersistedQueryNotFound error is returned. Example: curl -g ‘http://localhost:8080/graphql/?extensions={“persistedQuery”:{“sha256Hash”:“b952c19b894e1aa89dc05b7d53e15ab34ee0b3a3f11cdf3486acef4f0fe85c52”}}‘

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Usage with Apollo

You can create an Apollo GraphQL client with persisted queries enabled. In the background, Apollo sends the same requests like the ones previously shown. For example: 
import { createPersistedQueryLink } from "apollo-link-persisted-queries";
import { createHttpLink } from "apollo-link-http";
import { InMemoryCache } from "apollo-cache-inmemory";
import ApolloClient from "apollo-client";
const link = createPersistedQueryLink().concat(createHttpLink({ uri: "/graphql" }));
const client = new ApolloClient({
  cache: new InMemoryCache(),
  link: link,
});
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