---
id: 5921c995-292b-4dac-afa5-75d58507bf5e
---

# Imbalanced data distribution in a MongoDB sharded cluster.
---

This incident type occurs when a MongoDB sharded cluster experiences an imbalance in the distribution of data across its shards. Sharding is a method of horizontally partitioning data across multiple servers to improve performance and scalability. However, if the distribution of data is uneven, it can lead to slower queries and poor performance. This can happen due to a variety of reasons, such as uneven data growth, uneven write patterns, or improper shard key selection. It is important to monitor and rebalance the data distribution periodically to ensure optimal performance.

### Parameters
```shell
export HOSTNAME="PLACEHOLDER"

export PORT="PLACEHOLDER"

export MONGODB_CONNECTION_STRING="PLACEHOLDER"

export DATABASE="PLACEHOLDER"

export COLLECTION="PLACEHOLDER"
```

## Debug

### Check the status of the MongoDB sharded cluster
```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "sh.status()"
```

### Check the status of the individual MongoDB shards
```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "sh.status({verbose:true})"
```

### Check the distribution of data across MongoDB shards
```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "db.collection.getShardDistribution()"
```

### Check the amount of data stored on each MongoDB shard
```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "db.collection.totalSize()"
```

## Repair

### Rebalance the data across the MongoDB shards
```shell
bash

#!/bin/bash



# Set the MongoDB connection string

MONGODB_CONN_STR=${MONGODB_CONNECTION_STRING}



# Enable the balancer if it's not already enabled

mongo $MONGODB_CONN_STR --eval 'sh.setBalancerState(true)'



# Wait for the balancer to finish any ongoing operations

mongo $MONGODB_CONN_STR --eval 'sh.waitForBalancer()'



# Rebalance the data across the shards

mongo $MONGODB_CONN_STR --eval 'sh.rebalanceCollection("${DATABASE}.${COLLECTION}")'



# Disable the balancer once the rebalancing is complete

mongo $MONGODB_CONN_STR --eval 'sh.setBalancerState(false)'


```


This incident type occurs when a MongoDB sharded cluster experiences an imbalance in the distribution of data across its shards. Sharding is a method of horizontally partitioning data across multiple servers to improve performance and scalability. However, if the distribution of data is uneven, it can lead to slower queries and poor performance. This can happen due to a variety of reasons, such as uneven data growth, uneven write patterns, or improper shard key selection. It is important to monitor and rebalance the data distribution periodically to ensure optimal performance.


```shell
export HOSTNAME="PLACEHOLDER"

export PORT="PLACEHOLDER"

export MONGODB_CONNECTION_STRING="PLACEHOLDER"

export DATABASE="PLACEHOLDER"

export COLLECTION="PLACEHOLDER"
```


### Check the status of the MongoDB sharded cluster

```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "sh.status()"
```

### Check the status of the individual MongoDB shards

```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "sh.status({verbose:true})"
```

### Check the distribution of data across MongoDB shards

```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "db.collection.getShardDistribution()"
```

### Check the amount of data stored on each MongoDB shard

```shell
mongo --host ${HOSTNAME} --port ${PORT} --eval "db.collection.totalSize()"
```


### Rebalance the data across the MongoDB shards

```shell
bash

#!/bin/bash



# Set the MongoDB connection string

MONGODB_CONN_STR=${MONGODB_CONNECTION_STRING}



# Enable the balancer if it's not already enabled

mongo $MONGODB_CONN_STR --eval 'sh.setBalancerState(true)'



# Wait for the balancer to finish any ongoing operations

mongo $MONGODB_CONN_STR --eval 'sh.waitForBalancer()'



# Rebalance the data across the shards

mongo $MONGODB_CONN_STR --eval 'sh.rebalanceCollection("${DATABASE}.${COLLECTION}")'



# Disable the balancer once the rebalancing is complete

mongo $MONGODB_CONN_STR --eval 'sh.setBalancerState(false)'


```


Imbalanced data distribution in a MongoDB sharded cluster.

Overview

Parameters

Debug

Check the status of the MongoDB sharded cluster

Check the status of the individual MongoDB shards

Check the distribution of data across MongoDB shards

Check the amount of data stored on each MongoDB shard

Repair

Rebalance the data across the MongoDB shards

Learn more

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