# MongoDB 4

This page describes the Optimization Pack for MongoDb version 4.x.

## Metrics

### Document operations

| Name                         | Unit        | Description                                                    |
| ---------------------------- | ----------- | -------------------------------------------------------------- |
| mongodb\_document\_deleted   | documents/s | The average number of documents deleted per second             |
| mongodb\_documents\_inserted | documents/s | The average number of documents inserted per second            |
| mongodb\_documents\_updated  | documents/s | The average number of documents updated per second             |
| mongodb\_documents\_returned | documents/s | The average number of documents returned by queries per second |

### Other metrics

| Name                                  | Unit        | Description                                                                                                                       |
| ------------------------------------- | ----------- | --------------------------------------------------------------------------------------------------------------------------------- |
| mongodb\_connections\_current         | connections | The current number of opened connections                                                                                          |
| mongodb\_heap\_used                   | bytes       | The total size of heap space used (only available in Linux/Unix systems)                                                          |
| mongodb\_mem\_used                    | bytes       | The total amount of memory used                                                                                                   |
| mongodb\_page\_faults\_total          | faults/s    | The average number of page faults per second (i.e., operations that require MongoDB to access data on disk rather than on memory) |
| mongodb\_global\_lock\_current\_queue | ops         | The current number of operations queued because of a lock                                                                         |

## Parameters

### Cache

| Name                              | Unit       | Type    | Default                                                                                                                                         | Domain                                                                                                                                          | Restart | Description                                                                                                                     |
| --------------------------------- | ---------- | ------- | ----------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------- |
| mongodb\_cache\_size              | megabytes  | Integer | You should select your own default value when you create a study, since it is highly dependent on your system (how much memory your system has) | You should select your own default value when you create a study, since it is highly dependent on your system (how much memory your system has) | No      | The maximum size of the internal cache that MongoDB (WiredTiger) will use to operate                                            |
| mongodb\_eviction\_trigger        | percentage | Integer | 95                                                                                                                                              | 1 → 99                                                                                                                                          | No      | The percentage threshold on the use of the MongoDB cache for which cache eviction will start and client threads will throttle   |
| mongodb\_eviction\_target         | percentage | Integer | 80                                                                                                                                              | 1 → 99                                                                                                                                          | No      | The target percentage usage of the MongoDB cache to reach after evictions                                                       |
| mongodb\_eviction\_dirty\_trigger | percentage | Integer | 20                                                                                                                                              | 1 → 99                                                                                                                                          | No      | The percentage threshold on the use of MongoDB dirty cache for which cache eviction will start and client threads will throttle |
| mongodb\_eviction\_dirty\_target  | percentage | Integer | 5                                                                                                                                               | 1 → 99                                                                                                                                          | No      | The target percentage usage of the MongoDB dirty cache to reach after evictions                                                 |
| mongodb\_eviction\_threads\_min   | threads    | Integer | 4                                                                                                                                               | 1 → 20                                                                                                                                          | No      | The minimum number of threads to use to perform cache eviction                                                                  |
| mongodb\_eviction\_threads\_max   | threads    | Integer | 4                                                                                                                                               | 1 → 20                                                                                                                                          | No      | The maximum number of threads to use to perform cache eviction                                                                  |

### Other parameters

| Name                 | Unit    | Type    | Default | Domain      | Restart | Description                                                                                    |
| -------------------- | ------- | ------- | ------- | ----------- | ------- | ---------------------------------------------------------------------------------------------- |
| mongodb\_sync\_delay | seconds | Integer | 1min    | 1min → 6min | no      | The temporal interval between fsync operations where mongod flushes its working memory to disk |

## Constraints

Here are some constraints on parameters of MongoDB 4 that avoid common errors in the configuration of a MongoDB deployment:

| Constraint                                                         |
| ------------------------------------------------------------------ |
| mongodb\_eviction\_threads\_min <= mongodb\_eviction\_threads\_max |
| mongodb\_eviction\_dirty\_target <= mongodb\_eviction\_target      |
| mongodb\_eviction\_dirty\_trigger <= mongodb\_eviction\_trigger    |