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<p><strong>Critical issues/regressions fixed:</strong></p>
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<ul><li><a href="https://jira.mongodb.org/browse/WT-4324" target="_blank" rel="noreferrer noopener">WT-4324</a>&nbsp;Ensure checkpoints rewrite pages with data in the future (potential data loss)</li><li><a href="https://jira.mongodb.org/browse/SERVER-39932" target="_blank" rel="noreferrer noopener">SERVER-39932</a>&nbsp;SessionRuntimeInfo memory is not being released (<a href="https://jira.mongodb.org/browse/STAR-235" target="_blank" rel="noreferrer noopener">STAR-235</a>)</li></ul>
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<p><strong>Sharding:</strong></p>
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<ul><li><a href="https://jira.mongodb.org/browse/SERVER-35219" target="_blank" rel="noreferrer noopener">SERVER-35219</a>&nbsp;Regain MongoDB balancer performance with sessions</li><li><a href="https://jira.mongodb.org/browse/SERVER-39847" target="_blank" rel="noreferrer noopener">SERVER-39847</a>&nbsp;Migrating session info can trigger fassert when destination shard has transaction history truncated by oplog</li></ul>
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<p><strong>Replication:</strong></p>
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<ul><li><a href="https://jira.mongodb.org/browse/SERVER-37255" target="_blank" rel="noreferrer noopener">SERVER-37255</a>&nbsp;replSetReconfig with concurrent election can trigger invariant</li><li><a href="https://jira.mongodb.org/browse/SERVER-38722" target="_blank" rel="noreferrer noopener">SERVER-38722</a>&nbsp;CollectionCloner should handle QueryPlanKilled on collection drop</li><li><a href="https://jira.mongodb.org/browse/SERVER-39490" target="_blank" rel="noreferrer noopener">SERVER-39490</a>&nbsp;opWriteConcernCounters can cause undefined behavior due to overflow</li></ul>
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<p><strong>Storage/WT:</strong></p>
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<ul><li><a href="https://jira.mongodb.org/browse/SERVER-17010" target="_blank" rel="noreferrer noopener">SERVER-17010</a>&nbsp;Reduce file handle usage in File based Sorter</li><li><a href="https://jira.mongodb.org/browse/SERVER-36437" target="_blank" rel="noreferrer noopener">SERVER-36437</a>&nbsp;The dbstats command should lock the database in MODE_IS instead of MODE_S</li><li><a href="https://jira.mongodb.org/browse/WT-4615" target="_blank" rel="noreferrer noopener">WT-4615</a>&nbsp;Sync backup file before returning backup cursor (until this fix, we fsync neither the backup file nor the directory where it's located)</li></ul>
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<p><strong>Diagnostics:</strong></p>
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<ul><li><a href="https://jira.mongodb.org/browse/SERVER-37722" target="_blank" rel="noreferrer noopener">SERVER-37722</a>&nbsp;Quiet mode does not suppress connection end events</li><li><a href="https://jira.mongodb.org/browse/SERVER-40131" target="_blank" rel="noreferrer noopener">SERVER-40131</a>&nbsp;Incorrect format string in Windows stacktrace generator.</li></ul>
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