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raft: don't propose config changes with regressed lead support #132150

Merged
merged 3 commits into from
Oct 16, 2024
Merged

raft: don't propose config changes with regressed lead support #132150

merged 3 commits into from
Oct 16, 2024

Commits on Oct 16, 2024

  1. raft: rename confchange_v2_add_double_implicit to _single_ 

    The test was only adding a single node, so the name was misleading.

Epic: None
Release note: None
    @nvanbenschoten
    nvanbenschoten committed Oct 16, 2024
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  2. raft: use 3x replication in confchange_v2_add_single_implicit 

    This commit updates the confchange_v2_add_single_implicit test to start
with 2 nodes so that the addition of a third voter does not regress the
lead support and trip up the automatic transition out of the joint
configuration.

Epic: None
Release note: None
    @nvanbenschoten
    nvanbenschoten committed Oct 16, 2024
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  3. raft: don't propose config changes with regressed lead support 

    Fixes cockroachdb#125355.

If the lead support has not caught up from the previous configuration,
we must not propose another configuration change. Doing so would
compromise the lead support promise made by the previous configuration
and used as an expiration of a leader lease. Instead, we wait for the
lead support under the current configuration to catch up to the maximum
lead support reached under the previous config. If the lead support is
never able to catch up, the leader will eventually step down due to
CheckQuorum.

As a reminder, if we reject a config change, it will be reproposed again
shortly, at which point the lead support will likely have caught up.

As a second reminder, we fortify both voters and learners. We also
always add new replicas as learners before promoting them to voters. The
combination here means that a leader will commonly already be supported
a voter when it is promoted added to the lead support computation.

Release note: None
    @nvanbenschoten
    nvanbenschoten committed Oct 16, 2024
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