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sougou 2015-11-30 17:54:51 -08:00
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@ -28,7 +28,9 @@ If the application already has a well-distributed sharding key, you just have to
#### Hashed sharding key
If the application's sharding key is a monotonically increasing number, then you may not get well-balanced shards. In such cases, you can ask V3 to route queries based on the hash of the main sharding key.
Vitess's filtered replication currently requires that the hash value be physically present as a column in each table. To satisfy this need, you still need to create a column to store this hash value. However, V3 will take care of populating this on your behalf. *We will soon be removing this restriction once we change filtered replication to also perform the same hashing.*
Vitess's filtered replication currently requires that the hash value be physically present as a column in each table. To satisfy this need, you still need to create a column to store this hash value. However, V3 will take care of populating this on your behalf.
*We will soon be removing this restriction once we change filtered replication to also perform the same hashing.*
#### Auto-increment columns
When a table gets sharded, you are no longer able to use MySQL's auto increment functionality. V3 allows you to designate a table in an unsharded database as the source of auto-increment ids. Once you've specified this, V3 will transparently use generated values from this table to keep the auto-increment going. The auto-increment can column can in turn be a basic or hashed sharding key. If it's a hashed sharding key, the newly generated value will be hashed before the query is routed.