Hi,
I've got some issues/misunderstanding of AVRO schema evolution.
When reading through avro documentation, for example [1], I understood,
that schema evolution is supported, and if I added column with specified
default, it should be backwards compatible (and even forward when I remove
it again). Sounds great, so I added column defined as:
{
"name": "newColumn",
"type": ["null","string"],
"default": null,
"doc": "something wrong"
}
and try to consumer some topic having this schema from beginning, it fails
with message:
Caused by: java.lang.ArrayIndexOutOfBoundsException: 5
at
org.apache.avro.io.parsing.Symbol$Alternative.getSymbol(Symbol.java:424)
at
org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:290)
at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
at
org.apache.avro.io.ResolvingDecoder.readIndex(ResolvingDecoder.java:267)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:179)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:232)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:222)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:175)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:179)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:232)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:222)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:175)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:145)
at
tech.allegro.schema.json2avro.converter.JsonAvroConverter.convertToJson(JsonAvroConverter.java:83)
to give a little bit more information. Avro schema defines one top level
type, having 2 fields. String describing type of message, and union of N
types. All N-1, non-modified types can be read, but one updated with
optional, default-having column cannot be read. I'm not sure if this design
is strictly speaking correct, but that's not the point (feel free to
criticise and recommend better approach!). I'm after schema evolution,
which seems not to be working.
And if we alter type definition to:
"type": "string",
"default": ""
it still does not work and generated error is:
Caused by: org.apache.avro.AvroRuntimeException: Malformed data. Length is
negative: -1
at org.apache.avro.io.BinaryDecoder.doReadBytes(BinaryDecoder.java:336)
at org.apache.avro.io.BinaryDecoder.readString(BinaryDecoder.java:263)
at
org.apache.avro.io.ResolvingDecoder.readString(ResolvingDecoder.java:201)
at
org.apache.avro.generic.GenericDatumReader.readString(GenericDatumReader.java:422)
at
org.apache.avro.generic.GenericDatumReader.readString(GenericDatumReader.java:414)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:181)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:232)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:222)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:175)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:179)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:232)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:222)
at
org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:175)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:145)
at
tech.allegro.schema.json2avro.converter.JsonAvroConverter.convertToJson(JsonAvroConverter.java:83)
Am I doing something wrong?
thanks,
Martin.
[1]
https://docs.oracle.com/database/nosql-12.1.3.4/GettingStartedGuide/schemaevolution.html#changeschema-rules
