# Best Practices For Secondary Indexes

__*Indexing best practices*__

+ The more secondary indexes, the better? **It's not. **
+ Which column might be suitable for indexing? ** appears in the WHERE predicate and has a high cardinality. **

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Secondary indexes can speed up query, but adding indexes has side effects. The previous section introduced the storage model for indexes. For each additional index, there will be one more key-value when you insert a piece of data.

Therefore, the more indexes you have, the slower the write and the more space it takes up. In addition, too many indexes can affect the optimizer's runtime, and inappropriate indexes can mislead the optimizer. Therefore, more secondary indexes don't mean better performance.