What causes "Can't get generic schema for topic " in apache/pulsar?

Check the logged cause (attr topic/version) to see the underlying ExecutionException reason

apache/pulsar · error · RuntimeException

Can't get generic schema for topic…

Error message

Can't get generic schema for topic <schemaInfoProvider.getTopicName()>

What it means

AbstractMultiVersionReader.read wraps the reader-cache lookup (getSchemaReader -> readerCache.get) which can fail with ExecutionException while resolving the schema for a version. The original cause is logged and a RuntimeException 'Can't get generic schema for topic X' is thrown, meaning the generic schema reader could not be built for the message's schema version on that topic.

Solutions

Check the logged cause (attr topic/version) to see the underlying ExecutionException reason
Verify the schema still exists on the topic (pulsar-admin schemas get)
Recreate/reset the consumer so it fetches current schema versions
Ensure the client can reach the broker and has schema read permissions
If the schema was deleted, re-upload the schema or use a reader schema compatible with old data

Example fix

// before
T value = multiVersionReader.read(messageData); // RuntimeException
// after
try {
    T value = multiVersionReader.read(messageData);
} catch (RuntimeException e) {
    log.warn("Generic schema unavailable for topic {}, falling back", topic, e);
    // re-fetch schema / reconnect consumer
}

Defensive patterns

Strategy: try-catch

Validate before calling

byte[] latest = ((PulsarClientImpl) client).getSchemaLookupService();
// ensure topic schema exists before reading:
// pulsar-admin schemas get <topic> or SchemaInfoProvider fetch of current version

Type guard

null

Try / catch

try {
    T value = multiVersionReader.read(messageData);
} catch (RuntimeException e) {
    if (e.getMessage().startsWith("Can't get generic schema")) {
        log.warn("Schema reader unavailable for topic {}, version mismatch", topic, e);
        // refresh consumer / re-upload schema
    } else {
        throw e;
    }
}

Prevention

Never delete topic schemas while consumers still read old data
Verify schema versions exist with pulsar-admin schemas get before consuming
Monitor broker connectivity and schema registry health
Set an appropriate reader schema to tolerate version drift

When it happens

Trigger: Calling read(byte[]/ByteBuf) when the reader cache loader throws while fetching schema info for the message's schema version — e.g. the schema version does not exist, the broker returns an error, or the schema info provider fails asynchronously.

Common situations: Schema was deleted from the topic while old messages still exist; broker connectivity/permission problems during schema lookup; consumer reading data written before a schema change whose version is no longer retrievable; corrupted schema version bytes.

Related errors

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/5f40e21af3892576. Report an issue: GitHub.

Appendix: source

Thrown at pulsar-client/src/main/java/org/apache/pulsar/client/impl/schema/reader/AbstractMultiVersionReader.java:79

        return providerSchemaReader.read(bytes);
    }

    @Override
    public T read(InputStream inputStream) {
        return providerSchemaReader.read(inputStream);
    }

    @Override
    public T read(InputStream inputStream, byte[] schemaVersion) {
        try {
            return schemaVersion == null ? read(inputStream) :
                    getSchemaReader(schemaVersion).read(inputStream);
        } catch (ExecutionException e) {
            log.error().attr("topic", schemaInfoProvider.getTopicName())
                    .attr("version", Hex.encodeHexString(schemaVersion))
                    .exception(e)
                    .log("Can't get generic schema");
            throw new RuntimeException("Can't get generic schema for topic " + schemaInfoProvider.getTopicName());
        }
    }

    public SchemaReader<T> getSchemaReader(byte[] schemaVersion) throws ExecutionException {
        return readerCache.get(BytesSchemaVersion.of(schemaVersion));
    }

    @Override
    public T read(byte[] bytes, byte[] schemaVersion) {
        try {
            return schemaVersion == null ? read(bytes) :
                    getSchemaReader(schemaVersion).read(bytes);
        } catch (ExecutionException | AvroTypeException e) {
            if (e instanceof AvroTypeException) {
                throw new SchemaSerializationException(e);
            }
            log.error().attr("topic", schemaInfoProvider.getTopicName())
                    .attr("version", Hex.encodeHexString(schemaVersion))

View on GitHub (pinned to 820761864e)