{"record":{"id":"86c542615a15b402","repo":"apache/cassandra","slug":"cannot-find-comparator-for-component","errorCode":null,"errorMessage":"Cannot find comparator for component ","messagePattern":"Cannot find comparator for component ","errorType":"validation","errorClass":"MarshalException","httpStatus":null,"severity":"error","filePath":"src/java/org/apache/cassandra/db/marshal/DynamicCompositeType.java","lineNumber":520,"sourceCode":"            {\n                // ByteBufferUtil.string failed.\n                // Log it here and we'll further throw an exception below since comparator == null\n                logger.error(\"Failed when decoding the byte buffer in ByteBufferUtil.string()\", ce);\n            }\n            catch (Exception e)\n            {\n                // parse failed.\n                // Log it here and we'll further throw an exception below since comparator == null\n                logger.error(\"Failed to parse value string \\\"{}\\\" with exception:\", valueStr, e);\n            }\n        }\n        else\n        {\n            comparator = aliases.get((byte)(header & 0xFF));\n        }\n\n        if (comparator == null)\n            throw new MarshalException(\"Cannot find comparator for component \" + i);\n        else\n            return comparator;\n    }\n\n    public ByteBuffer decompose(Object... objects)\n    {\n        throw new UnsupportedOperationException();\n    }\n\n    @Override\n    public boolean isCompatibleWith(AbstractType<?> previous)\n    {\n        if (this == previous)\n            return true;\n\n        if (!(previous instanceof DynamicCompositeType))\n            return false;\n","sourceCodeStart":502,"sourceCodeEnd":538,"githubUrl":"https://github.com/apache/cassandra/blob/88fd0f6a0eaed8943f05ac9e8f947882b8ddc8f1/src/java/org/apache/cassandra/db/marshal/DynamicCompositeType.java#L502-L538","documentation":"After decoding the header, DynamicCompositeType must resolve a concrete comparator: either the named class (bytes) or an alias byte (header & 0xFF). If the alias is not present in the type's alias map (e.g. aliases defined as 'a->IntType' and data uses 'z') or the named class cannot be resolved to a comparator, this MarshalException is thrown. It means the data references a comparator the type does not know about.","triggerScenarios":"Validating a DynamicCompositeType value whose component alias byte has no registered alias, or whose comparator class name doesn't resolve; typically when reading old data after the aliases definition in the schema changed.","commonSituations":"The DynamicCompositeType alias string in the schema was edited (aliases removed/renamed) after data was written; reading SSTables produced with different alias definitions; hand-built buffers with bogus alias bytes.","solutions":["Restore/add the missing alias to the DynamicCompositeType definition in the schema (e.g. ALTER with aliases covering all bytes present in the data)","Identify the alias byte from the error context and ensure the schema maps it to the intended type (e.g. 'z->UUIDType')","If the comparator class name path failed, verify the referenced AbstractType class exists in this Cassandra version"],"exampleFix":"// before\nDynamicCompositeType.getInstance(ascii->UTF8Type)\n// after (data contains alias byte 'b')\nDynamicCompositeType.getInstance(ascii->UTF8Type, b->Int32Type)","handlingStrategy":"validation","validationCode":"// before writing, confirm every alias byte used is declared in the schema\ndef checkAliases(typeDef, aliasBytes) { return aliasBytes.every(b -> typeDef.aliases.containsKey(b)); }","typeGuard":null,"tryCatchPattern":"try { type.validate(buffer); } catch (MarshalException e) { log.error(\"Unknown comparator alias/class in composite value\", e); }","preventionTips":["Never remove or rename aliases in a DynamicCompositeType definition once data exists","Document which alias bytes are reserved","Version schema changes and backfill/rewrite data referencing old aliases"],"tags":["cassandra","composite-type","schema"],"backgroundTag":"resource-not-found","analyzedSha":"88fd0f6a0eaed8943f05ac9e8f947882b8ddc8f1","analyzedAt":"2026-09-10T07:29:22.284Z","contentChangedAt":"2026-09-10T07:29:22.284Z","schemaVersion":2},"datasetVersion":"2026-09-14T16:17:12.679Z"}