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I was asked specifically about WiredTigerKVEngine::cleanShutdown and the places where MongoDB configures compatibility versions for WiredTiger.
For the purposes of unblocking this work, we should set compatibility=(require_min="3.1") (was 3.1.0) to determine whether starting with FCV=4.0. References to earlier WT versions should be removed. Since compatibility is omitted to enable the latest behavior in WiredTiger, none of these changes need to wait for the WiredTiger version to be bumped.
When downgrading (to 4.0) as part of clean shutdown, if downgrading:
- we should remove any use_timestamp configuration to WT_CONNECTION::close (the default behavior should be correct for 4.1 and above)
- we should remove the loop that calls WiredTigerUtil::setTableLogging
- we should not need to close / reopen and then close again.
- Instead, it should be sufficient to call _conn->reconfigure with compatibility=(release=3.1) with just one call to _conn->close
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