Spark streaming Dynamic Schema Evolution from Kafka Eventhub on Microbatch - apache-spark

We are streaming data from the Kafka Eventhub. The records may have a nested structure. The schema is inferred dynamically from the data and the Delta table is formed with the schema of the first incoming batch of data.
Note: The data read from Kafka topic will be a whole JSON string. Hence,
When we apply schema and convert to a dataframe, we lose the fields' values with mismatch datatype or newly added fields.
When we do spark.read.json, the entire field values are converted to String.
We encounter a situation where the Source data has some schema changes. Some of the scenarios we faced are :
The datatype changes at the parent level
The datatype changes at the nested level
There are duplicate keys in a different case
There are the addition of new fields
A sample Source data with the Actual schema
{
"Id": "101",
"Name": "John",
"Department": {
"Id": "Dept101",
"Name": "Technology",
"EmpId": "10001"
},
"Experience": 2,
"Organization": [
{
"Id": "Org101",
"Name": "Google"
},
{
"Id": "Org102",
"Name": "Microsoft"
}
]
}
A sample Source data addressing the 4 points mentioned above
{
"Id": "102",
"name": "Rambo", --- Point 3
"Department": {
"Id": "Dept101",
"Name": "Technology",
"EmpId": 10001 ---- Point 2
},
"Experience": "2", --- Point 1
"Organization": [
{
"Id": "Org101",
"Name": "Google",
"Experience": "2", --- Point 4
},
{
"Id": "Org102",
"Name": "Microsoft",
"Experience": "2",
}
]
}
We need a solution to overcome the above issues. Though it's difficult to embed the new schema to the existing delta table, at least we should be able to separate the records with schema changes without losing the original data.

Related

Merge documents by fields

I have two types of docs. Main docs and additional info for it.
{
"id": "371"
"name": "Mike",
"location": "Paris"
},
{
"id": "371-1",
"age": 20,
"lastname": "Piterson"
}
I need to merge them by id, to get result doc. The result should look like:
{
"id": "371"
"name": "Mike",
"location": "Paris"
"age": 20,
"lastname": "Piterson"
}
Using COLLECT / INTO, SPLIT(), and MERGE():
FOR doc IN collection
COLLECT id = SPLIT(doc.id, '-')[0] INTO groups
RETURN MERGE(MERGE(groups[*].doc), {id})
Result:
[
{
"id": "371",
"location": "Paris",
"name": "Mike",
"lastname": "Piterson",
"age": 20
}
]
This will:
Split each id attribute at any - and return the first part
Group the results into sepearate arrays (groups)
Merge #1: Merge all objects into one
Merge #2: Merge the id into the result
See REMOVE & INSERT or REPLACE for write operations.

kafka-connect : Error in sink cassandra connector

I get a runtime Error for a sink cassandra connector, I try to pick data form kafka and store it in cassandra, You find the error stack below :
{
"name": "cassandraSinkConnector2",
"connector": {
"state": "RUNNING",
"worker_id": "localhost:8083"
},
"tasks": [
{
"id": 0,
"state": "FAILED",
"worker_id": "localhost:8083",
"trace": "org.apache.kafka.connect.errors.ConnectException: Exiting WorkerSinkTask due to unrecoverable exception.\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:560)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:321)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:224)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:192)\n\tat org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:175)\n\tat org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:219)\n\tat java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)\n\tat java.util.concurrent.FutureTask.run(FutureTask.java:266)\n\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)\n\tat java.lang.Thread.run(Thread.java:748)\nCaused by: org.apache.kafka.connect.errors.DataException: Key must be a struct or map. This connector requires that records from Kafka contain the keys for the Cassandra table. Please use a transformation like org.apache.kafka.connect.transforms.ValueToKey to create a key with the proper fields.\n\tat io.confluent.connect.cassandra.CassandraSinkTask.put(CassandraSinkTask.java:94)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:538)\n\t... 10 more\n"
}
],
"type": "sink"
}
I used the distributed configuration below for my connector:
{
"name": "cassandraSinkConnector2",
"config": {
"connector.class": "io.confluent.connect.cassandra.CassandraSinkConnector",
"tasks.max": "1",
"topics": "appartenance_de",
"cassandra.contact.points": "localhost",
"cassandra.kcql": "INSERT INTO app_test SELECT * FROM app_de",
"cassandra.port": "9042",
"cassandra.keyspace": "dev_dkks",
"cassandra.username": "superuser",
"cassandra.password": "superuser",
"cassandra.write.mode": "upsert",
"value.converter.schemas.enable": "true",
"value.converter": "io.confluent.connect.avro.AvroConverter",
"value.converter.schema.registry.url": "http://localhost:8081",
"transforms": "createKey,extractInt",
"transforms.createKey.type": "org.apache.kafka.connect.transforms.ValueToKey",
"transforms.createKey.fields": "id",
"transforms.extractInt.type": "org.apache.kafka.connect.transforms.ExtractField$Key",
"transforms.extractInt.field": "id",
"name": "cassandraSinkConnector2"
},
"tasks": [
{
"connector": "cassandraSinkConnector2",
"task": 0
}
],
"type": "sink"
Per my answer here, the error you're seeing is
org.apache.kafka.connect.errors.DataException:
Record with a null key was encountered. This connector requires that records from Kafka contain the keys for the Cassandra table.
Please use a transformation like org.apache.kafka.connect.transforms.ValueToKey to create a key with the proper fields.
I'd suggest using a Single Message Transform as suggested in the error to correctly key your data. You can see an example of doing this here and the documentation for the transform here.

The datum is not an example of schema- Avro Python

avro.schema.Parse works fine. The values to the data are read correctly. But looks like data and schema doesn't sync in.
I get the error:
The datum {datafromfile{whole bunch fields from data}, DATE = value, file_name = value}
is not an example of the schema from the .avsc file.
My schema is a nested avro schema. ***The last field of type 'info' contains some fields of type strings but not all the fields as in the data coming in.
Is this mismatch between fields causing an issue?
Below is my .avsc file.
{
"type": "record",
"name": "header_data",
"doc": "A list of strings.",
"fields": [
{"name": "DATE", "type": "string"},
{"name": "file_name", "type": "string"},
{"name": "info", "type": "info"}]
}

Azure ADF sliceIdentifierColumnName is not populating correctly

I've set up a ADF pipeline using a sliceIdentifierColumnName which has worked well as it populated the field with a GUID as expected. Recently however this field stopped being populated, the refresh would work but the sliceIdentifierColumnName field would have a value of null, or occasionally the load would fail as it attempted to populate this field with a value of 1 which causes the slice load to fail.
This change occurred at a point in time, before it worked perfectly, after it repeatedly failed to populate the field correctly. I'm sure no changes were made to the Pipeline which caused this to suddenly fail. Any pointers where I should be looking?
Here an extract of the pipeline source, I'm reading from a table in Amazon Redshift and writing to an Azure SQL table.
"activities": [
{
"type": "Copy",
"typeProperties": {
"source": {
"type": "RelationalSource",
"query": "$$Text.Format('select * from mytable where eventtime >= \\'{0:yyyy-MM-ddTHH:mm:ssZ}\\' and eventtime < \\'{1:yyyy-MM-ddTHH:mm:ssZ}\\' ' , SliceStart, SliceEnd)"
},
"sink": {
"type": "SqlSink",
"sliceIdentifierColumnName": "ColumnForADFuseOnly",
"writeBatchSize": 0,
"writeBatchTimeout": "00:00:00"
}
},
"inputs": [
{
"name": "AmazonRedshiftSomeName"
}
],
"outputs": [
{
"name": "AzureSQLDatasetSomeName"
}
],
"policy": {
"timeout": "1.00:00:00",
"concurrency": 10,
"style": "StartOfInterval",
"longRetry": 0,
"longRetryInterval": "00:00:00"
},
"scheduler": {
"frequency": "Hour",
"interval": 2
},
"name": "Activity-somename2Hour"
}
],
Also, here is the error output text
Copy activity encountered a user error at Sink:.database.windows.net side: ErrorCode=UserErrorInvalidDataValue,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=Column 'ColumnForADFuseOnly' contains an invalid value '1'.,Source=Microsoft.DataTransfer.Common,''Type=System.ArgumentException,Message=Type of value has a mismatch with column typeCouldn't store <1> in ColumnForADFuseOnly Column.
Expected type is Byte[].,Source=System.Data,''Type=System.ArgumentException,Message=Type of value has a mismatch with column type,Source=System.Data,'.
Here is part of the source dataset, it's a table with all datatypes as Strings.
{
"name": "AmazonRedshiftsomename_2hourly",
"properties": {
"structure": [
{
"name": "eventid",
"type": "String"
},
{
"name": "visitorid",
"type": "String"
},
{
"name": "eventtime",
"type": "Datetime"
}
}
Finally, the target table is identical to the source table, mapping each column name to its counterpart in Azure, with the exception of the additional column in Azure named
[ColumnForADFuseOnly] binary NULL,
It is this column which is now either being populated with NULLs or 1.
thanks,
You need to define [ColumnForADFuseOnly] as binary(32), binary with no length modifier is defaulting to a length of 1 and thus truncating your sliceIdentifier...
When n is not specified in a data definition or variable declaration statement, the default length is 1. When n is not specified with the CAST function, the default length is 30. See here

How to search through data with arbitrary amount of fields?

I have the web-form builder for science events. The event moderator creates registration form with arbitrary amount of boolean, integer, enum and text fields.
Created form is used for:
register a new member to event;
search through registered members.
What is the best search tool for second task (to search memebers of event)? Is ElasticSearch well for this task?
I wrote a post about how to index arbitrary data into Elasticsearch and then to search it by specific fields and values. All this, without blowing up your index mapping.
The post is here: http://smnh.me/indexing-and-searching-arbitrary-json-data-using-elasticsearch/
In short, you will need to do the following steps to get what you want:
Create a special index described in the post.
Flatten the data you want to index using the flattenData function:
https://gist.github.com/smnh/30f96028511e1440b7b02ea559858af4.
Create a document with the original and flattened data and index it into Elasticsearch:
{
"data": { ... },
"flatData": [ ... ]
}
Optional: use Elasticsearch aggregations to find which fields and types have been indexed.
Execute queries on the flatData object to find what you need.
Example
Basing on your original question, let's assume that the first event moderator created a form with following fields to register members for the science event:
name string
age long
sex long - 0 for male, 1 for female
In addition to this data, the related event probably has some sort of id, let's call it eventId. So the final document could look like this:
{
"eventId": "2T73ZT1R463DJNWE36IA8FEN",
"name": "Bob",
"age": 22,
"sex": 0
}
Now, before we index this document, we will flatten it using the flattenData function:
flattenData(document);
This will produce the following array:
[
{
"key": "eventId",
"type": "string",
"key_type": "eventId.string",
"value_string": "2T73ZT1R463DJNWE36IA8FEN"
},
{
"key": "name",
"type": "string",
"key_type": "name.string",
"value_string": "Bob"
},
{
"key": "age",
"type": "long",
"key_type": "age.long",
"value_long": 22
},
{
"key": "sex",
"type": "long",
"key_type": "sex.long",
"value_long": 0
}
]
Then we will wrap this data in a document as I've showed before and index it.
Then, the second event moderator, creates another form having a new field, field with same name and type, and also a field with same name but with different type:
name string
city string
sex string - "male" or "female"
This event moderator decided that instead of having 0 and 1 for male and female, his form will allow choosing between two strings - "male" and "female".
Let's try to flatten the data submitted by this form:
flattenData({
"eventId": "F1BU9GGK5IX3ZWOLGCE3I5ML",
"name": "Alice",
"city": "New York",
"sex": "female"
});
This will produce the following data:
[
{
"key": "eventId",
"type": "string",
"key_type": "eventId.string",
"value_string": "F1BU9GGK5IX3ZWOLGCE3I5ML"
},
{
"key": "name",
"type": "string",
"key_type": "name.string",
"value_string": "Alice"
},
{
"key": "city",
"type": "string",
"key_type": "city.string",
"value_string": "New York"
},
{
"key": "sex",
"type": "string",
"key_type": "sex.string",
"value_string": "female"
}
]
Then, after wrapping the flattened data in a document and indexing it into Elasticsearch we can execute complicated queries.
For example, to find members named "Bob" registered for the event with ID 2T73ZT1R463DJNWE36IA8FEN we can execute the following query:
{
"query": {
"bool": {
"must": [
{
"nested": {
"path": "flatData",
"query": {
"bool": {
"must": [
{"term": {"flatData.key": "eventId"}},
{"match": {"flatData.value_string.keyword": "2T73ZT1R463DJNWE36IA8FEN"}}
]
}
}
}
},
{
"nested": {
"path": "flatData",
"query": {
"bool": {
"must": [
{"term": {"flatData.key": "name"}},
{"match": {"flatData.value_string": "bob"}}
]
}
}
}
}
]
}
}
}
ElasticSearch automatically detects the field content in order to index it correctly, even if the mapping hasn't been defined previously. So, yes : ElasticSearch suits well these cases.
However, you may want to fine tune this behavior, or maybe the default mapping applied by ElasticSearch doesn't correspond to what you need : in this case, take a look at the default mapping or, for even further control, the dynamic templates feature.
If you let your end users decide the keys you store things in, you'll have an ever-growing mapping and cluster state, which is problematic.
This case and a suggested solution is covered in this article on common problems with Elasticsearch.
Essentially, you want to have everything that can possibly be user-defined as a value. Using nested documents, you can have a key-field and differently mapped value fields to achieve pretty much the same.

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