# MongoDB Performance<br />ch3 Index Operations

###### tags: `MongoDB University M201`

## Building Indexes

* Foreground indexes are fase, but block operations
* Background indexes are slow, but don't block operations

:::warning
For feature compatibility version (fcv) =="4.2", all index builds use an optimized build process== that holds the exclusive lock only at the beginning and end of the build process. The rest of the build process yields to interleaving read and write operations. **MongoDB ignores the background option if specified.**
:::

* currentOp()
* killOp(<opid>)

## Understanding Explain

Using explain is best way to analyze what heppen when the query executed even without the query being executed.

db.<collection>.explain('<argument>')

#### argument
* queryPlanner (default)
* not actual executed
* executionStats
* actual executed
* allPlansExecution
* actual executed

Sort_key_generator: in memory sort
If a sort uses more than 32 mb, then the server is going to cancel that query

## Hint()

To select the index to query manually

db.people.find(
    { name: 'John Doe', zipCode: { $gt: '63000' } }
).hint (
    'index_name'
)

## Resource Allocation for Indexes

* Determine Index Size
* Resource Allocation
* Edge Case

### Determine Index Size

* db.stats()
* db.<collection>.stats()

### Resource Allocation

* Disk
* Memory (RAM)

// get memory size in cache
let stats = db.<collection>.stats({1'indexDetail: true'})
stats.indexDetails.endstation_name_1.cache

### Edge Case

* Occasional Reports
* Right-end-side index increments

## Basic Benchmarking

Types of Performance Benchmarking
* Public test suite
* Specific or Private Testing environment

Low Level Benchmarking
* File I/O Performance
* Scheduler Performance
* Memory allocation and transfer speed
* Thread performance
* Database server performance
* Translation Isolation
* ...

Database server Benchmarking
* Data set load
* Writes per second
* Reads per second
* Balanced work loads
* Read/Write ratio

Distributed Systems Benchmarking
* Linearization
* Serialization
* Fault tolerance