Refresh Iceberg Table metadata every 2 minutes instead of before each intermediate file written

[JayajP]

When we use the Iceberg Sink with the BLMS Catalog, refreshing the table metadata uses a BLMS Read Quota. The default quota is 300 read requests a second.

• Currently, send a read request before every intermediate file we write to ensure the partition spec is up to date. This exhausts the BLMS Read quota for pipelines with non-trivial load.
• After this PR we will only reload the Iceberg Table metadata every 2 minutes per-worker. Now a dataflow job with 100 workers will only use 50 out of the 300 read requests a minute.

Tested through unit tests and a by launching a pipeline. https://screenshot.googleplex.com/BdB7Nqx2EUYeUZo

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[gemini-code-assist]

Summary of Changes

Hello @JayajP, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a performance bottleneck in the Iceberg Sink when interacting with the BLMS Catalog. Previously, table metadata was refreshed excessively, leading to frequent exhaustion of read quotas. The core change introduces a time-based caching mechanism that refreshes table metadata only once every two minutes per worker, drastically reducing the load on the catalog and improving the stability of data pipelines.

Highlights

• Optimized Iceberg Metadata Refresh: The frequency of refreshing Iceberg table metadata has been changed from 'before every intermediate file write' to 'every 2 minutes per worker'.
• Reduced BLMS Read Quota Usage: This change significantly lowers the number of read requests to the BLMS Catalog, preventing quota exhaustion in high-load pipelines.
• Introduced Time-Based Caching: A new LastRefreshedTable class and LAST_REFRESHED_TABLE_CACHE now manage table objects, refreshing them only when metadata is considered stale (older than 3 minutes).

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[JayajP]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces an intelligent caching mechanism for Iceberg table metadata to reduce read requests to the catalog. Instead of refreshing before every intermediate file write, metadata is now refreshed only when it's considered stale (every few minutes). This is achieved by wrapping the Table object in a new LastRefreshedTable class that tracks the last refresh time and uses a time-based threshold with double-checked locking to decide when to refresh. The changes are logical and include relevant unit tests to verify the new behavior. My only feedback is a minor point of consistency between the code and the pull request description.

[JayajP]

R: @ahmedabu98

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[ahmedabu98]

LGTM

Did you experiment with a few different staleness threshold values?

[JayajP]

No, I only checked at 2 minutes. This seemed like a safe value since a job with 100 workers would only consume 1/6th of the default read quota. Project's with larger usages would likely have quota overrides.

[ahmedabu98]

Sounds good, let's get this in for now and see how users react (if they prefer a quicker refresh interval or not)