Introduction — juxt/crux-kafka 19.09-1.5.0-alpha

Introduction

Crux offers a small REST API that allows you to send transactions and run queries over HTTP. For instance, you could deploy your Crux nodes along with Kafka into a Kubernetes pod running on AWS and interact with Crux from your application purely via HTTP. Using Crux in this manner is a valid use-case but it cannot support all of the features and benfits that running the Crux node inside of your application provides.

Your application only needs to communicate with one Crux node when using the REST API. This Crux node may placed be behind a load balancer which spreads the load over multiple nodes transparently to application. In addition, different Crux nodes might be still be catching up with the head of the transaction log, and since different queries might go to different nodes, you have to be conscious of read consistency issues when designing your application to use Crux in this way. Fortunately, you can mitigate read consistency issues the ability to query consistent point-in-time snapshots of the database by specifying temporal coordinates along with your queries.

The REST API also provides an experimental endpoint for SPARQL 1.1 Protocol queries under /sparql/, rewriting the query into the Crux Datalog dialect. Only a small subset of SPARQL is supported and no other RDF features are available.

Using the HTTP API

The HTTP interface is provided as a Ring middleware in a Clojure namespace, located at crux/crux-http-server/src/crux/http_server.clj. There is an example of using this middleware in a full example HTTP server configuration: https://github.com/juxt/crux/tree/master/docs/example/standalone_webservice

Whilst CORS may be easily configured for use while prototyping a Single Page Application that uses Crux directly from a web browser, it is currently NOT recommended to expose Crux directly to any untrusted endpoints (including web browsers) in production since the default query API does not sandbox or otherwise restrict the execution of queries.

Index

Table 1. API
uri	method	description
`/`	GET	returns various details about the state of the database
`/document/[content-hash]`	GET or POST	returns the document for a given hash
`/documents`	POST	returns a map of document ids and respective documents for a given set of content hashes submitted in the request body
`/entity`	POST	Returns an entity for a given ID and optional valid-time/transaction-time co-ordinates
`/entity-tx`	POST	Returns the `:put` or `:cas` transaction that most recently set a key
`/history/[:key]`	GET OR POST	Returns the transaction history of a key
`/query`	POST	Takes a datalog query and returns its results
`/query-stream`	POST	Same as `/query` but the results are streamed
`/sync`	GET	Wait until the Kafka consumer’s lag is back to 0
`/tx-log`	GET	Returns a list of all transactions
`/tx-log`	POST	The "write" endpoint, to post transactions.

GET `/`

Returns various details about the state of the database. Can be used as a health check.

curl -X GET $nodeURL/

{:crux.kv/kv-store "crux.kv.rocksdb.RocksKv",
 :crux.kv/estimate-num-keys 92,
 :crux.kv/size 72448,
 :crux.zk/zk-active? true,
 :crux.tx-log/consumer-state
   {:crux.kafka.topic-partition/crux-docs-0
      {:offset 25,
       :time #inst "2019-01-08T11:06:41.867-00:00",
       :lag 0},
    :crux.kafka.topic-partition/crux-transaction-log-0
      {:offset 19,
       :time #inst "2019-01-08T11:06:41.869-00:00",
       :lag 0}}}

estimate-num-keys is an (over)estimate of the number of transactions in the log (each of which is a key in RocksDB). RocksDB does not provide an exact key count.

GET/POST `/document/[content-hash]`

Returns the document stored under that hash, if it exists.

curl -X GET $nodeURL/document/7af0444315845ab3efdfbdfa516e68952c1486f2

{:crux.db/id :foobar, :name "FooBar"}

Hashes for older versions of a document can be obtained with /history-range or /history, under the :crux.db/content-hash keys.

GET/POST `/documents`

Returns a map from the documents ids to the documents for ids set. Possible to get map keys as #crux/id literals if preserve-crux-ids param is set to "true"

curl -X POST $nodeURL/documents \
     -H "Content-Type: application/edn" \
     -d '#{"7af0444315845ab3efdfbdfa516e68952c1486f2"}'

{"7af0444315845ab3efdfbdfa516e68952c1486f2" {:crux.db/id :foobar, :name "FooBar"}}

POST `/entity`

Takes a key and, optionally, a :valid-time and/or :transact-time (defaulting to now). Returns the value stored under that key at those times.

See Bitemporality for more information.

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '{:eid :tommy}' \
     $nodeURL/entity

{:crux.db/id :tommy, :name "Tommy", :last-name "Petrov"}

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '{:eid :tommy :valid-time #inst "1999-01-08T14:03:27.254-00:00"}' \
     $nodeURL/entity

nil

POST `/entity-tx`

Takes a key and, optionally, :valid-time and/or :transact-time (defaulting to now). Returns the :put or :cas transaction that most recently set that key at those times.

See Bitemporality for more information.

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '{:eid :foobar}' \
     $nodeURL/entity-tx

{:crux.db/id "8843d7f92416211de9ebb963ff4ce28125932878",
 :crux.db/content-hash "7af0444315845ab3efdfbdfa516e68952c1486f2",
 :crux.db/valid-time #inst "2019-01-08T16:34:47.738-00:00",
 :crux.tx/tx-id 0,
 :crux.tx/tx-time #inst "2019-01-08T16:34:47.738-00:00"}

GET/POST `/history/[:key]`

Returns the transaction history of a key, from newest to oldest transaction time.

curl -X GET $nodeURL/history/:ivan

[{:crux.db/id "a15f8b81a160b4eebe5c84e9e3b65c87b9b2f18e",
  :crux.db/content-hash "c28f6d258397651106b7cb24bb0d3be234dc8bd1",
  :crux.db/valid-time #inst "2019-01-07T14:57:08.462-00:00",
  :crux.tx/tx-id 14,
  :crux.tx/tx-time #inst "2019-01-07T16:51:55.185-00:00"}

 {...}]

POST `/query`

Takes a Datalog query and returns its results.

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '{:query {:find [e] :where [[e :last-name "Petrov"]]}}' \
     $nodeURL/query

#{[:boris][:ivan]}

Note that you are able to add :full-results? true to the query map to easily retrieve the source documents relating to the entities in the result set. For instance to retrieve all documents in a single query:

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '{:query {:find [e] :where [[e :crux.db/id _]] :full-results? true}}' \
     $nodeURL/query

POST `/query-stream`

Same as /query but the results are streamed.

GET `/sync`

Wait until the Kafka consumer’s lag is back to 0 (i.e. when it no longer has pending transactions to write). Timeout is 10 seconds by default, but can be specified as a parameter in milliseconds. Returns the transaction time of the most recent transaction.

curl -X GET $nodeURL/sync?timeout=500

#inst "2019-01-08T11:06:41.869-00:00"

GET `/tx-log`

Returns a list of all transactions, from oldest to newest transaction time.

curl -X GET $nodeURL/tx-log

({:crux.tx/tx-time #inst "2019-01-07T15:11:13.411-00:00",
  :crux.api/tx-ops [[
    :crux.tx/put "c28f6d258397651106b7cb24bb0d3be234dc8bd1"
    #inst "2019-01-07T14:57:08.462-00:00"]],
  :crux.tx/tx-id 0}

 {:crux.tx/tx-time #inst "2019-01-07T15:11:32.284-00:00",
  ...})

POST `/tx-log`

Takes a vector of transactions (any combination of :put, :delete, :cas and :evict) and executes them in order. This is the only "write" endpoint.

curl -X POST \
     -H "Content-Type: application/edn" \
     -d '[[:crux.tx/put {:crux.db/id :ivan, :name "Ivan" :last-name "Petrov"}],
          [:crux.tx/put {:crux.db/id :boris, :name "Boris" :last-name "Petrov"}],
          [:crux.tx/delete :maria  #inst "2012-05-07T14:57:08.462-00:00"]]' \
     $nodeURL/tx-log

{:crux.tx/tx-id 7, :crux.tx/tx-time #inst "2019-01-07T16:14:19.675-00:00"}