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  1. Core Server
  2. SERVER-40010

Shard secondaries with 4.0 binary and 3.6 FCV are calling `_flushDatabaseCacheUpdates`

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 4.0.6
    • 4.0.7
    • Sharding
    • None
    • Fully Compatible
    • ALL
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      Use a shard with 4.0 primary & 3.6 secondary and perform secondary reads with read concern local or majority.

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      Use a shard with 4.0 primary & 3.6 secondary and perform secondary reads with read concern local or majority .
    • Sharding 2019-03-25

    Description

      Currently, shard secondaries with 4.0 binary and 3.6 FCV call `_flushDatabaseCacheUpdates` against the primary node. This is wrong because the primary might be running a 3.6 binary, which doesn't have this command. As a result, in partial-upgrade cases, where a secondary node is on 4.0 and the primary is on 3.6 (with FCV 3.6), queries against the secondary will always fail with an error saying "CommandNotFound: no such command: '_flushDatabaseCacheUpdates'".

      For some context:

      • 3.6 - introduced the versioned secondary reads and the forceRoutingTableRefresh/_flushRoutingTableCacheUpdates commands
      • 4.0 - introduced the database version concept, which ensures that all commands which read/write database and collection metadata are routed appropriately after a movePrimary or drop/recreate. This logic introduced the _flushDatabaseCacheUpdates command, which is only on 4.0, but is unconditionally called if the catalog cache is accessed on a secondary node.

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            kaloian.manassiev@mongodb.com Kaloian Manassiev
            kaloian.manassiev@mongodb.com Kaloian Manassiev
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              Updated:
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