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Clear jumbo Flag

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If MongoDB cannot split a chunk that exceeds the specified chunk size, MongoDB labels the chunk as jumbo.

If the chunk size no longer exceeds the specified chunk size, MongoDB automatically clears the jumbo flag for the chunk when the mongos rewrites the chunk metadata.

In cases where you need to clear the flag manually, however, the following procedures outline the steps to manually clear the jumbo flag.

The preferred manual way to clear the jumbo flag from a chunk is to attempt to split the chunk. If the chunk is divisible, MongoDB removes the flag upon successful split of the chunk.

1

Connect mongosh to a mongos.

2

Run sh.status(true) to find the chunk labeled jumbo.

sh.status(true)

For example, the following output from sh.status(true) shows that chunk with shard key range { "x" : 2 } -->> { "x" : 4 } is jumbo.

--- Sharding Status ---
sharding version: {
...
}
shards:
...
databases:
...
test.foo
shard key: { "x" : 1 }
chunks:
shard-b 2
shard-a 2
{ "x" : { "$minKey" : 1 } } -->> { "x" : 1 } on : shard-b Timestamp(2, 0)
{ "x" : 1 } -->> { "x" : 2 } on : shard-a Timestamp(3, 1)
{ "x" : 2 } -->> { "x" : 4 } on : shard-a Timestamp(2, 2) jumbo
{ "x" : 4 } -->> { "x" : { "$maxKey" : 1 } } on : shard-b Timestamp(3, 0)
3

Use either sh.splitAt() or sh.splitFind() to split the jumbo chunk.

sh.splitAt( "test.foo", { x: 3 })

MongoDB removes the jumbo flag upon successful split of the chunk.

In some instances, MongoDB cannot split the no-longer jumbo chunk, such as a chunk with a range of single shard key value. As such, you cannot split the chunk to clear the flag.

In such cases, you can either change the shard key so that the chunk can become divisible or manually clear the flag.

Starting in 4.4, MongoDB provides the refineCollectionShardKey command. Using the refineCollectionShardKey command, you can refine a collection's shard key by adding a suffix field or fields to the existing key. By adding new field(s) to the shard key, indivisible jumbo chunks can become divisible.

1

Connect mongosh to a mongos.

2

Run sh.status(true) to find the chunk labeled jumbo.

sh.status(true)

For example, the following output from sh.status(true) shows that for the sharded collection test.orders, both the chunk with shard key range { "status" : "A" } -->> { "status" : "D" } and the chunk with range { "status" : "D" } -->> { "status" : "P" } are jumbo.

--- Sharding Status ---
sharding version: {
...
}
shards:
...
databases:
...
test.orders
shard key: { "status" : 1 }
unique: false
balancing: true
chunks:
shardA 2
shardB 2
{ "status" : { "$minKey" : 1 } } -->> { "status" : "A" } on : shardB Timestamp(3, 0)
{ "status" : "A" } -->> { "status" : "D" } on : shardA Timestamp(5, 1) jumbo
{ "status" : "D" } -->> { "status" : "P" } on : shardA Timestamp(4, 2) jumbo
{ "status" : "P" } -->> { "status" : { "$maxKey" : 1 } } on : shardB Timestamp(5, 0)
3

To address the low cardinality of the key status, refine the key for the test.orders collection. For example, add the order_id and customer_id fields as a suffix to the current shard key; i.e. the shard key will be { status: 1, order_id: 1, customer_id: 1 } after refinement.

  1. First, create the index to support the shard key { status: 1, order_id: 1, customer_id: 1 } if the index does not already exist.

    db.orders.createIndex( { status: 1, order_id: 1, customer_id: 1 } )

    For additional index considerations for refining the shard key, see Index Considerations.

  2. In the admin database, run the refineCollectionShardKey command to add the order_id and customer_id fields as a suffix to the existing key:

    db.adminCommand( {
    refineCollectionShardKey: "test.orders",
    key: { status: 1, order_id: 1, customer_id: 1 }
    } )

The refineCollectionShardKey command updates the chunk ranges and zone ranges to incorporate the new fields without modifying the range values of the existing key fields. That is, the refinement of the shard key does not immediately affect the distribution of chunks across shards or zones. Any future chunk splits or migration occur as part of the routine sharding operations.

Tip

After you refine the shard key, it may be that not all documents in the collection have the suffix field(s). To populate the missing shard key field(s), see Missing Shard Key Fields.

Before refining the shard key, ensure that all or most documents in the collection have the suffix fields, if possible, to avoid having to populate the field afterwards.

You can manually clear the flag using the following steps.

Important

If you clear the jumbo flag for a chunk that still exceeds the chunk size, MongoDB will re-label the chunk as jumbo when MongoDB tries to move the chunk.

Tip
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