Send only blocks at missing heights #5206
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When syncing chain information for blobs between validators, we were sending more data than necessary. The previous implementation would send **all blocks up to the height** where a blob was published, even when only the specific block containing that blob was needed. For sparse chains (chains with gaps in block heights), this meant sending many unnecessary blocks, wasting network bandwidth and validator processing time. Addresses #5205 (comment) ## Proposal This PR changes the blob synchronization strategy from "send all blocks up to height N" to "send only blocks at specific heights": 1. **Modified `send_chain_info_for_blobs`**: Instead of tracking the maximum height per chain, now collects a `BTreeSet` of all specific heights where blobs exist 2. **New method `send_chain_info_at_heights`**: Sends chain information only for the exact block heights specified, not all blocks leading up to those heights 3. **Updated documentation**: Clarifies that this optimization specifically benefits sparse chains ### Example Impact Previously, if blobs existed at heights [5, 10, 15] on a chain: - Sent blocks 0-5, 0-10, 0-15 (up to 30 blocks sent, with significant duplication) Now: - Sends only blocks at heights 5, 10, 15 (exactly 3 blocks) ## Test Plan - CI ## Release Plan - Nothing to do / These changes follow the usual release cycle. - Backport to `main`. ## Links - [reviewer checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)
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Backport of #5206 ## Motivation When syncing chain information for blobs between validators, we were sending more data than necessary. The previous implementation would send **all blocks up to the height** where a blob was published, even when only the specific block containing that blob was needed. For sparse chains (chains with gaps in block heights), this meant sending many unnecessary blocks, wasting network bandwidth and validator processing time. Addresses #5205 (comment) ## Proposal This PR changes the blob synchronization strategy from "send all blocks up to height N" to "send only blocks at specific heights": 1. **Modified `send_chain_info_for_blobs`**: Instead of tracking the maximum height per chain, now collects a `BTreeSet` of all specific heights where blobs exist 2. **New method `send_chain_info_at_heights`**: Sends chain information only for the exact block heights specified, not all blocks leading up to those heights 3. **Updated documentation**: Clarifies that this optimization specifically benefits sparse chains ### Example Impact Previously, if blobs existed at heights [5, 10, 15] on a chain: - Sent blocks 0-5, 0-10, 0-15 (up to 30 blocks sent, with significant duplication) Now: - Sends only blocks at heights 5, 10, 15 (exactly 3 blocks) ## Test Plan - CI ## Release Plan - Nothing to do / These changes follow the usual release cycle. ## Links - [reviewer checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist) Backport of #5206
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Motivation
When syncing chain information for blobs between validators, we were sending more data than necessary. The previous implementation would send all blocks up to the height where a blob was published, even when only the specific block containing that blob was needed.
For sparse chains (chains with gaps in block heights), this meant sending many unnecessary blocks, wasting network bandwidth and validator processing time.
Addresses #5205 (comment)
Proposal
This PR changes the blob synchronization strategy from "send all blocks up to height N" to "send only blocks at specific heights":
send_chain_info_for_blobs: Instead of tracking the maximum height per chain, now collects aBTreeSetof all specific heights where blobs existsend_chain_info_at_heights: Sends chain information only for the exact block heights specified, not all blocks leading up to those heightsExample Impact
Previously, if blobs existed at heights [5, 10, 15] on a chain:
Now:
Test Plan
Release Plan
main.Links