cancel
Showing results for 
Search instead for 
Did you mean: 
Data Engineering
Join discussions on data engineering best practices, architectures, and optimization strategies within the Databricks Community. Exchange insights and solutions with fellow data engineers.
cancel
Showing results for 
Search instead for 
Did you mean: 

Concurrency issue with append only writed

EDDatabricks
Contributor

Dear all,

We have a pyspark streaming job (DBR: 14.3) that continuously writes new data on a Delta Table (TableA).

On this table, there is a pyspark batch job (DBR: 14.3) that operates every 15 minuted and in some cases it may delete some records from TableA using a merge statement (WhenMatchedDelete construct with a business related condition). This condition identifies specific records that are already present in TableA and it is impossible to match with records that are written during query execution.

Periodically, we get exceptions due to concurrency issues with the following trace:

 

{
  "timestamp":1711718436569,
  "userId":"xxx",
  "userName":"xxx",
  "operation":"STREAMING UPDATE",
  "operationParameters":{
    "outputMode":"Append",
    "queryId":xxx,
    "epochId":xxx,
    "statsOnLoad":false
  },
  "job":{
  "jobId":"xxx",
  "jobName":"xxx",
  "jobRunId":"xxx",
  "runId":"xxx",
  "jobOwnerId":"xxx",
  "triggerType":"manual"
  },
  "notebook":{
    "notebookId":"xxx"
  },
  "clusterId":"xxx",
  "readVersion":21835,
  "isolationLevel":"WriteSerializable",
  "isBlindAppend":true,
  "operationMetrics":{
    "numRemovedFiles":"0",
    "numOutputRows":"50",
    "numOutputBytes":"25199",
    "numAddedFiles":"1"
  },
  "tags":{
    "restoresDeletedRows":"false",
    "delta.rowTracking.preserved":"true"
  },
  "engineInfo":"Databricks-Runtime/14.3.x-scala2.12",
  "txnId":"1eb445f1-2abd-4b6c-a8f0-3ccc1f2474f2"
}

 

 

As mentioned in this page: https://learn.microsoft.com/en-us/azure/databricks/optimizations/isolation-level, there should be no concurrency issue. Even after checking the limitations page (https://learn.microsoft.com/en-us/azure/databricks/optimizations/isolation-level#rlc-limitations) we follow all conditions
- No complex conditional clauses
- Explicit predicates that uniquely identify each record to be deleted

We suspect that this may have to do with this option: "delta.rowTracking.preserved":"true" but we were not able to locate any documentation about what this by default True configuration does. (only some github requests)

Please propose any mitigation actions for solving this concurrency issues as there may be some data inconsistencies to our ETL pipelines due to the aforementioned failures. Furthermore, this issue is not highlighted in the documentation per our understanding.

Thanks a-priori for your help.

Kind regards,
the European Dynamics team

2 REPLIES 2

Thanks for the fast reply @Retired_mod .

What we are unable to understand is that in the documentation it is specifically mentioned that
writes can not have issues in write serializable.

EDDatabricks_0-1712060583490.png

(https://learn.microsoft.com/en-us/azure/databricks/optimizations/isolation-level)

Kind regards,

The European Dynamics team

Dilisha
New Contributor II

Hi @EDDatabricks  - were you able to find the fix for this? I am also facing a similar issue. Added more details here  - Getting concurrent Append exception after upgradin... - Databricks Community - 76521

Connect with Databricks Users in Your Area

Join a Regional User Group to connect with local Databricks users. Events will be happening in your city, and you won’t want to miss the chance to attend and share knowledge.

If there isn’t a group near you, start one and help create a community that brings people together.

Request a New Group