DBA

常见问题分析

日志中找出慢查询

grep -P '\d+ms$' mongodb.log | grep DB.COLLECTION

性能调优

应用设计模式

• 只更新需要更新的字段 - 不建议取出整个文档，更新某个字段，然后保存整个文档

• 避免不存在的查询 - 不存在的字段会导致全表扫描

• Use covered queries when possible.

• Test every query in your application with explain()

• Update multiple array elements in a single operation

• Avoid scatter-gather queries

• Choose the appropriate write guarantees

• Choose the right read-concern

• Use causal consistency where needed

• Use the most recent drivers from MongoDB

• Ensure uniform distribution of shard keys

• Use hash-based sharding when appropriate

数据模型设计 & 索引

• Avoid large documents

• Avoid unnecessarily long fifield names

• Use caution when considering indexes on low-cardinality fifields

• Eliminate unnecessary indexes

• Remove indexes that are prefifixes of other indexes

• Use a compound index rather than index intersection

• Use partial indexes

• Avoid regular expressions that are not left anchored or rooted

• Use index optimizations available in the WiredTiger storage engine

• Understand any existing document schema – MongoDB Compass

• Identify & remove obsolete indexes

磁盘 I/O

• Readahead size should be set to 0 for WiredTiger

• Use XFS fifile systems; avoid EXT3

• Disable access time settings

• Don’t use Huge Pages

• Use RAID10

• Use multiple devices for different databases – WiredTiger.

• Implement multi-temperature storage & data locality using MongoDB Zones