Is there an API for Scylla Nodetool?

Guy · November 20, 2022, 7:58am

Question:
Is there an API for nodetool? Especially nodetool tablestats?
I saw there is scylladb/api/api-doc at master · scylladb/scylladb · GitHub. Is this the right place to look for APIs?

*The question was asked on Stack Overflow by SilentCanon

Guy · November 20, 2022, 8:00am

Answer:
The Scylla server indeed has a REST API and it’s documentation is at the URL you point to. You can find a Swagger UI when you start the Scylla server as well: https://docs.scylladb.com/operating-scylla/rest/.

But, please note that nodetool, for example, does not use the API directly. Instead, it talks to the Scylla JMX proxy, which is a Java process that implements Cassandra-compatible JMX API. You can still use the REST API directly, but you have to figure out the mapping between the JMX operations and the REST API yourself.

For something like nodetool tablestats, the first step is to check what JMX APIs nodetool uses:

github.com

scylladb/scylla-tools-java/blob/master/src/java/org/apache/cassandra/tools/nodetool/TableStats.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.apache.cassandra.tools.nodetool;

import java.util.*;

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The command delegates to TableStatsHolder class:

github.com

scylladb/scylla-tools-java/blob/master/src/java/org/apache/cassandra/tools/nodetool/stats/TableStatsHolder.java#L117


      
                      mpTable.put("dropped_mutations", table.droppedMutations);
          
          
            mpTables.put(table.name, mpTable);
                  }
                  mpKeyspace.put("tables", mpTables);
                  mpRet.put(keyspace.name, mpKeyspace);
              }
              return mpRet;
          }
          
          
private void initializeKeyspaces(NodeProbe probe, boolean humanReadable, boolean ignore, List<String> tableNames)
          {
              OptionFilter filter = new OptionFilter(ignore, tableNames);
              ArrayListMultimap<String, ColumnFamilyStoreMBean> selectedTableMbeans = ArrayListMultimap.create();
              Map<String, StatsKeyspace> keyspaceStats = new HashMap<>();
          
          
    // get a list of table stores
              Iterator<Map.Entry<String, ColumnFamilyStoreMBean>> tableMBeans = probe.getColumnFamilyStoreMBeanProxies();
          
          
    while (tableMBeans.hasNext())
              {

which uses the ColumnFamilyStoreMBean JMX API for querying table statistics.

You can find the implementation of the JMX API in the scylla-jmx project by finding the ColumnFamilyStore class (without the MBean suffix):

github.com

scylladb/scylla-jmx/blob/master/src/main/java/org/apache/cassandra/db/ColumnFamilyStore.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * Copyright 2015 Cloudius Systems

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From that class, you can see that, for example, the ColumnFamilyStore.getSSTableCountPerLevel() method delegates to the column_family/sstables/per_level/<table name> REST API URL.

*The answer was provided on Stack Overflow by Pekka Enberg

alix_F · December 6, 2022, 8:39pm

Hey, thanks for the answer but i’d like to ask more. If you know, or could point me at the direction of how to divide the actual scylla and the scylla-jmx. Meaning we wanted to get rid of cassandra on hosts just because it uses java, and it’s a huge package almost 30mb in size, while our goal was to make a tiniest distro possible. Is it possible to, let’s say, start scylla on the host and jmx nodetool services in a container on the same host, so API ports are reachable from inside the container? This way we would have no need for java in the initial distro and therefore on hosts

Yaniv_Kaul · December 7, 2022, 2:35pm

We have not done that, but we’ll be looking at this direction in the future - makes total sense to separate them.

alix_F · December 7, 2022, 8:43pm

Thank you for the quick response. Is there an approximate date you may look in to it, maybe in your backlog? So i would know when to get back to the though of replacing cassandra again?

Yaniv_Kaul · December 8, 2022, 11:41am

It’s not urgent. Besides being large and perhaps the need to update more often, it’s not a hassle. Splitting it has consequences that we’ll have to deal with. For example, running multiple containers side-by-side.

alix_F · December 8, 2022, 12:19pm

Have heard you. Thanks anyway!