# Limitations and considerations

When replicating to a SingleStore target, the following limitations apply:

* Due to the way SingleStore operates, when loading data to a SingleStore target during a Full Load task, duplicate key errors will not be reported to the logs.

* Updating the Primary Key is not supported as the Primary Key columns in SingleStore also serve as the shard key.

* When updating a column's value to its existing value, a zero rows affected is returned from SingleStore (unlike Oracle and Microsoft SQL Server, for example, that perform an update of one row). This generates an entry in the `attrep_apply_exceptions` control table and the following warning:

  ` Some changes from the source database had no impact when applied to the target database. See attrep_apply_exceptions table for details.  `

* Columnstore tables without a Primary Key or Unique Index are not supported.

* UPDATEs to a source column's data type or size will not be captured when the Create columnstore tables option is enabled [in the Advanced tab](https://help.qlik.com/en-US/replicate/November2024/Content/Replicate/Main/MemSQL/memsql_advanced_prop_mysql_target.htm).

  Information note

  Such UPDATEs *can* be performed on the target using a global or table transformation.

* Replicating data with 4-byte emoji characters is not supported.