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Add bugfix to v4.4.1 release notes

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Jack Grigg 2021-06-09 23:40:32 +01:00
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commit 41a21cab89
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doc/release-notes/release-notes-4.4.1.md
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Notable changes
===============
Fixed chain sync stall bug
--------------------------
The 4.3.0 release included a change to prevent redundant `getheaders` P2P
requests, to reduce node bandwith usage. This behaviour could be disable by
setting the config option `-nooptimize-getheaders`.
It turns out that these redundant requests were masking an unrelated bug in the
chain-rewinding logic that is used when the node detects a change to the
consensus rules (for example, if a user forgets to upgrade their `zcashd` node
before a network upgrade activates, and temporarily follows an un-upgraded chain
before restarting with the latest version).
In certain uncommon scenarios, a node could end up in a situation where it would
believe that the best header it knew about was more than 160 blocks behind its
actual best-known block. The redundant `getheaders` requests meant that this did
not cause an issue, because the node would continue requesting headers until it
found new blocks. After the `getheaders` optimizations, if a peer returned a
`headers` message that was entirely known to the node, it would stop requesting
more headers from that peer; this eventually caused node synchronization to
stall. Restarting with the `-nooptimize-getheaders` config option would enable
the node to continue syncing.
This release fixes the bug at its source, but the `-nooptimize-getheaders`
config option remains available if necessary.
Build system changes
--------------------