Topic Writer Backpressure

[vgvoleg]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Fixes: #694
Fixes: #137
Fixes: #136

What is the new behavior?

Other information

[Copilot]

Pull request overview

This PR introduces configurable backpressure for the Topic Writer by adding a byte-size limit for the internal in-flight buffer and making writes block (up to a timeout) until space is freed by server acks.

Changes:

• Add max_buffer_size_bytes and buffer_wait_timeout_sec to writer settings and enforce them in WriterAsyncIOReconnector.write_with_ack_future().
• Add a new public exception TopicWriterBufferFullError surfaced via ydb.topic.
• Add sync/async tests and an example showing how to use the buffer limit.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ydb/topic.py	Exports the new TopicWriterBufferFullError as part of the public Topic API.
ydb/_topic_writer/topic_writer.py	Adds settings fields, new exception type, and a helper for message size accounting.
ydb/_topic_writer/topic_writer_asyncio.py	Implements buffer accounting + backpressure wait loop and updates ack handling/shutdown behavior.
ydb/_topic_writer/topic_writer_test.py	Adds sync writer tests around error propagation/blocking behavior.
ydb/_topic_writer/topic_writer_asyncio_test.py	Adds async tests for timeout, ack-unblocking, and concurrent waiting writers.
examples/topic/writer_example.py	Documents how to configure and handle backpressure in user code.

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Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

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Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

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