Constraints

Table 1 shows the constraints designed to ensure the stability and security of UGO.

**Table 1** Function constraints
Function	Constraints
Pre-migration	Database service commands, such as SQLPlus command PROMPT, are not supported. There are some dynamic constraints in target databases, such as RDS for MySQL and GaussDB(for MySQL). For example, the total size of all Varchar* columns cannot exceed 64,000.
Object collection	System objects starting with SYS_PLSQL are not collected. Objects containing back quotes and blank characters cannot be collected, parsed, evaluated, converted, or migrated. Deleted objects starting with BIN$ are not collected. Oracle nested tables are not collected. Schema objects within the user permission scope are not collected. For details about other objects that are not collected, see Which of Schemas in the Oracle Databases Are Ignored for Migration?
SQL conversion	For command line and online converter usage scenarios, you need to input SQL according to the source database syntax documentation. Because current SQL Parser or Identifier checks the syntax of input SQL with respect to source database syntax documentation, it cannot match with source database engine functionality completely due to certain dynamic behavior.
Maximum number of connections to the source database	UGO occupies session connections of the source database. If the number of connections occupied by UGO exceeds the upper limit of connections to the source database, some workloads will be unable to access the source database. It will affect source database functions.
Source database object collection	Collecting objects using UGO occupies source database resources. You are advised to do this operation during off-peak hours.
No incremental data migration performed	UGO converts database schemas based on the collected data. Any schema changes after the data is collected will not be migrated. After the migration, the changes must be synchronized between the source and target databases, or, the changed functions will be affected.
Migration and verification	UGO is used to reduce costs and improve migration efficiency. After database objects are migrated, strict tests must be performed to ensure that the functions and performance of the migrated objects on the target database meet service requirements. Otherwise, the target database cannot be used to replace the source database.