Add BigQueryTableStreamingBufferEmptySensor for safe DML operations

[Arunodoy18]

This sensor checks if a BigQuery table's streaming buffer is empty before allowing DML operations (UPDATE, DELETE, MERGE) to proceed.

Solves the issue where DML statements fail with 'would affect rows in the streaming buffer' error when tables receive continuous streaming inserts.

Added comprehensive tests and example DAG demonstrating usage.

Description

This PR adds BigQueryTableStreamingBufferEmptySensor to solve a critical issue affecting users who run DML operations on BigQuery tables populated via streaming inserts.

User Impact

When Apache Airflow DAGs execute DML statements (UPDATE, DELETE, MERGE) on BigQuery tables that receive continuous streaming inserts (via Dataflow, CDC pipelines, BigQuery Storage Write API, or tabledata.insertAll), tasks fail with:

This causes:

• ❌ Pipeline failures requiring manual intervention
• ❌ Wasted compute resources on repeated retries
• ❌ Delayed data processing (hours of retry attempts)
• ❌ SLA violations in production environments
• ❌ Fragile pipelines requiring workarounds (sleep commands, external scripts)

Root Cause

BigQuery's documented limitation: DML operations cannot modify rows still residing in the streaming buffer. The buffer typically flushes within minutes but can take up to 90 minutes under certain conditions.

Airflow's current behavior: Operators like BigQueryInsertJobOperator immediately execute DML statements without checking buffer state, causing:

1. Job fails with streaming buffer error
2. Airflow retries the task (same error)
3. Repeated failures until buffer happens to be empty
4. No visibility into why failures occur or when it's safe to retry

Why This Matters

This issue is increasingly common because:

• Modern data pipelines heavily use streaming ingestion (real-time CDC, event streams, IoT data)
• BigQuery recommends streaming API for high-throughput ingestion
• Users need to run incremental DML operations (deduplication, status updates, soft deletes) on the same tables
• Google Cloud Composer users report this as a frequent pain point

Solution

What This PR Adds

A new sensor BigQueryTableStreamingBufferEmptySensor that:

1. Checks streaming buffer state via BigQuery Tables API
2. Waits until buffer is empty before allowing downstream DML operations
3. Provides visibility through logging (estimated rows in buffer)
4. Follows Airflow patterns (poke_interval, timeout, mode='reschedule')
5. Non-blocking when using mode='reschedule' (frees worker slots)

Implementation Details

class BigQueryTableStreamingBufferEmptySensor(BaseSensorOperator):
    """
    Checks if a BigQuery table's streaming buffer is empty.
    
    The sensor queries table metadata and checks the streamingBuffer field:
    - If streamingBuffer is None → buffer empty → sensor succeeds
    - If streamingBuffer exists → checks estimated_rows → waits
    """

closes **59408

[Arunodoy18]

I have solved this issue , For any misconduct do tell me so that i can make the following changes.
Thank you

[Copilot]

Pull request overview

This PR adds BigQueryTableStreamingBufferEmptySensor to address a critical issue where DML operations (UPDATE, DELETE, MERGE) fail on BigQuery tables that receive continuous streaming inserts. The sensor checks if the streaming buffer is empty before allowing downstream DML operations to proceed, preventing the "would affect rows in the streaming buffer" error.

Key changes:

• New sensor class that monitors BigQuery table streaming buffer state via the BigQuery Tables API
• Comprehensive unit tests covering success scenarios (no buffer, buffer with data)
• Example DAG demonstrating sensor usage with DML operations

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
providers/google/src/airflow/providers/google/cloud/sensors/bigquery.py	Implements BigQueryTableStreamingBufferEmptySensor with poke method that checks streaming buffer status using BigQueryHook
providers/google/tests/unit/google/cloud/sensors/test_bigquery.py	Adds test class with three unit tests covering sensor behavior when buffer is empty, when buffer has rows, and table reference construction
example_bigquery_streaming_buffer.py	Provides example DAG showing sensor usage before DML operations with recommended settings (reschedule mode, appropriate timeouts)

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[shahar1]

Please address failed tests and my comment - thanks!

[shahar1]

Should there be a specific if statement for that check, or does it only log it? Comment is a bit confusing, I'd remove it if it only logs.

[kaxil]

@Arunodoy18 I am going to close your PRs -- Please review and test your changes with correct PR description. Using LLMs without those increase maintenance burdens and CI run time.

Feel free to recreate focussed PRs following those guidelines.