---
id: 91a02e72-4ae2-4178-b49d-863d731fc8cb
---

# High Oplog Size Causing Storage Pressure in MongoDB
---

This incident type refers to a situation where the oplog size in MongoDB has increased significantly and is causing storage pressure. Oplog is the operation log that records all the write operations on a MongoDB instance. When the oplog size becomes too large, it can lead to storage pressure on the system, causing slow performance and even system crashes. It is important to monitor the oplog size and take appropriate actions to avoid this incident type.

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

export NUMBER_OF_DAYS="PLACEHOLDER"

export COLLECTION_NAME="PLACEHOLDER"

export DATABASE_NAME="PLACEHOLDER"

export OPLOG_SIZE_LIMIT_IN_MB="PLACEHOLDER"
```

## Debug

### Check disk usage
```shell
df -h
```

### Check MongoDB version
```shell
mongod --version
```

### Check the size of the collections in the database
```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.getCollectionInfos({},{size:true})"
```

### Check the size of the oplog
```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "printjson(db.getReplicationInfo())"
```

### Check the total size of the database
```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "printjson(db.stats())"
```

### Check the indexes on the collections
```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.collection.getIndexes()"
```

### Check the active connections in the database
```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.currentOp(true)"
```

### Check the logs for any errors or warnings
```shell
tail /var/log/mongodb/mongod.log
```

## Repair

### Implement a data retention policy to delete old data from the database and oplog. This can help in reducing the amount of data being stored and free up storage space for new data.
```shell


#!/bin/bash



# Set retention period in days

retention_period=${NUMBER_OF_DAYS}



# Set database name

database_name=${DATABASE_NAME}



# Set collection name

collection_name=${COLLECTION_NAME}



# Set oplog size limit in MB

oplog_size_limit=${OPLOG_SIZE_LIMIT_IN_MB}



# Create a timestamp for the retention period

timestamp=$(date -d "$retention_period days ago" +%s)



# Delete old data from the collection

mongo $database_name --eval "db.$collection_name.deleteMany({timestamp: {\$lt: $timestamp}})"



# Reduce the oplog size

mongo $database_name --eval "db.runCommand({replSetResizeOplog: 1, size: $oplog_size_limit})"



echo "Data retention policy has been implemented successfully."


```

This incident type refers to a situation where the oplog size in MongoDB has increased significantly and is causing storage pressure. Oplog is the operation log that records all the write operations on a MongoDB instance. When the oplog size becomes too large, it can lead to storage pressure on the system, causing slow performance and even system crashes. It is important to monitor the oplog size and take appropriate actions to avoid this incident type.


```shell
export MONGODB_CONNECTION_STRING="PLACEHOLDER"

export NUMBER_OF_DAYS="PLACEHOLDER"

export COLLECTION_NAME="PLACEHOLDER"

export DATABASE_NAME="PLACEHOLDER"

export OPLOG_SIZE_LIMIT_IN_MB="PLACEHOLDER"
```


### Check disk usage

```shell
df -h
```

### Check MongoDB version

```shell
mongod --version
```

### Check the size of the collections in the database

```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.getCollectionInfos({},{size:true})"
```

### Check the size of the oplog

```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "printjson(db.getReplicationInfo())"
```

### Check the total size of the database

```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "printjson(db.stats())"
```

### Check the indexes on the collections

```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.collection.getIndexes()"
```

### Check the active connections in the database

```shell
mongo ${MONGODB_CONNECTION_STRING} --eval "db.currentOp(true)"
```

### Check the logs for any errors or warnings

```shell
tail /var/log/mongodb/mongod.log
```


### Implement a data retention policy to delete old data from the database and oplog. This can help in reducing the amount of data being stored and free up storage space for new data.

```shell


#!/bin/bash



# Set retention period in days

retention_period=${NUMBER_OF_DAYS}



# Set database name

database_name=${DATABASE_NAME}



# Set collection name

collection_name=${COLLECTION_NAME}



# Set oplog size limit in MB

oplog_size_limit=${OPLOG_SIZE_LIMIT_IN_MB}



# Create a timestamp for the retention period

timestamp=$(date -d "$retention_period days ago" +%s)



# Delete old data from the collection

mongo $database_name --eval "db.$collection_name.deleteMany({timestamp: {\$lt: $timestamp}})"



# Reduce the oplog size

mongo $database_name --eval "db.runCommand({replSetResizeOplog: 1, size: $oplog_size_limit})"



echo "Data retention policy has been implemented successfully."


```


High Oplog Size Causing Storage Pressure in MongoDB

Overview

Parameters

Debug

Check disk usage

Check MongoDB version

Check the size of the collections in the database

Check the size of the oplog

Check the total size of the database

Check the indexes on the collections

Check the active connections in the database

Check the logs for any errors or warnings

Repair

Implement a data retention policy to delete old data from the database and oplog. This can help in reducing the amount of data being stored and free up storage space for new data.

Learn more

Related Runbooks

Support