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  1. Core Server
  2. SERVER-46093

Check read preference document for unknown options

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Details

    • Improvement
    • Status: Backlog
    • Major - P3
    • Resolution: Unresolved
    • None
    • None
    • None
    • Service Arch 2020-03-09, Service Arch 2020-03-23, Service Arch 2020-04-06, Service arch 2020-04-20, Service arch 2020-05-04, Service arch 2020-05-18, Service arch 2020-06-01, Service arch 2020-06-15, Service arch 2020-06-29, Service arch 2020-07-13, Service Arch 2020-07-27, Service Arch 2020-08-10, Service Arch 2020-08-24

    Description

      While writing the driver spec for hedged reads, we noticed that unsupported read preference options are silently ignored. This can produce unexpected behaviour when a user specifies the hedge option against a non-4.4 server: the option is silently ignored and no read hedging will be performed. For example, this is a read command with hedge option set run against a 4.2 server:

      MongoDB Enterprise mongos> db.runCommand({count: 'test', $readPreference: { mode: 'secondary', hedge: {asdf: true} }})
      {
      	"shards" : {
      		
      	},
      	"n" : 0,
      	"ok" : 1,
      	"operationTime" : Timestamp(1581060684, 2),
      	"$clusterTime" : {
      		"clusterTime" : Timestamp(1581060684, 2),
      		"signature" : {
      			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
      			"keyId" : NumberLong(0)
      		}
      	}
      }
      

      In contrast, the server will return an error document if the hedge document contains an unknown option. The following example was run against a 4.3.3 server:

      MongoDB Enterprise mongos> db.runCommand({count: 'test', $readPreference: { mode: 'secondary', hedge: {asdf: true} }})
      {
      	"ok" : 0,
      	"errmsg" : "BSON field 'hedge.asdf' is an unknown field.",
      	"code" : 40415,
      	"codeName" : "Location40415",
      	"operationTime" : Timestamp(1581060865, 1),
      	"$clusterTime" : {
      		"clusterTime" : Timestamp(1581060865, 1),
      		"signature" : {
      			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
      			"keyId" : NumberLong(0)
      		}
      	}
      }
      

      Acceptance criteria:

      The server should return an error document when an unknown read preference option is encountered.

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            backlog-server-sharding-nyc Backlog - Sharding NYC
            andreas.braun@mongodb.com Andreas Braun
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            Dates

              Created:
              Updated: