apache/cassandra · error · IllegalArgumentException

Can not parse replication factor %s

Error message

Can not parse replication factor %s

What it means

Nodetool's CMSAdmin (nodetool cms reconfigure) accepts replication factors of the form 'dc:rf'. If the argument contains more than one colon (more than 2 splits), it cannot be interpreted as a datacenter:replication-factor pair, so an IllegalArgumentException is thrown before any cluster operation starts.

Source

Thrown at src/java/org/apache/cassandra/tools/nodetool/CMSAdmin.java:188

                    if (args.size() > 1)
                        throw new IllegalArgumentException("Simple placement can only specify a single replication factor across all data centers");
                    int parsedRf;
                    try
                    {
                        parsedRf = Integer.parseInt(args.get(0));
                    }
                    catch (Throwable t)
                    {
                        throw new IllegalArgumentException(String.format("Can not parse replication factor from %s", args.get(0)));
                    }
                    probe.getCMSOperationsProxy().reconfigureCMS(parsedRf);
                    return;
                }
                else
                {
                    String[] splits = rf.split(":");
                    if (splits.length > 2)
                        throw new IllegalArgumentException(String.format("Can not parse replication factor %s", rf));
                    String dc = splits[0];
                    int parsedRf;
                    try
                    {
                        parsedRf = Integer.parseInt(splits[1]);
                    }
                    catch (Throwable t)
                    {
                        throw new IllegalArgumentException(String.format("Can not parse replication factor from %s", args.get(0)));
                    }
                    parsedRfs.put(dc, parsedRf);
                }
            }

            probe.getCMSOperationsProxy().reconfigureCMS(parsedRfs);
        }
    }

View on GitHub (pinned to 88fd0f6a0e)

Solutions

  1. Pass replication factors as separate dc:rf pairs, e.g. `nodetool cms reconfigure dc1:3 dc2:5`, not a single colon-heavy string
  2. Quote arguments correctly in the shell so stray colons from variables are not concatenated
  3. Check `nodetool describecluster` for the actual DC names and format each as dc:integer

Example fix

// before
nodetool cms reconfigure "dc1:3:dc2:5"
// after
nodetool cms reconfigure dc1:3 dc2:5
Defensive patterns

Strategy: validation

Validate before calling

String rf = args.get(0);
String[] splits = rf.split(":");
if (splits.length > 2 || splits.length < 2)
    throw new IllegalArgumentException("expected dc:rf, got " + rf);
Integer.parseInt(splits[1]); // fail fast

Try / catch

try { probe.getCMSOperationsProxy().reconfigureCMS(parsedRfs); }
catch (IllegalArgumentException e) { System.err.println("Bad RF spec: " + e.getMessage()); }

Prevention

When it happens

Trigger: Running `nodetool cms reconfigure` with an RF argument containing multiple colons, e.g. `nodetool cms reconfigure dc1:5:extra` or a stray quoted string with colons.

Common situations: Typos when specifying per-DC RFs, accidentally passing a full option string, or pasting config snippets containing 'keyspace:dc:rf'-style values instead of the expected 'dc:rf' pair.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/49ee801ab3867aba. Report an issue: GitHub.