在不同数据库之间迁移时，经常需要考虑如何处理Large binary objects (LOBs)

如果需要迁移LOB，可以使用以下模式：

  • Full LOB mode – DMS会迁移所有数据，由于不知道最大LOB是多少，LOB只能一个一个的迁移，迁移起来很慢
  • Limited LOB mode - 规定一个最大值，超出这个值的数据将被截断。这种模式下，迁移速度大大提升。一般建议使用这种模式，并将最大值设置为100M
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Note

With Oracle, LOBs are treated as VARCHAR data types whenever possible. This approach means that AWS DMS fetches them from the database in bulk, which is significantly faster than other methods. The maximum size of a VARCHAR in Oracle is 32 K. Therefore, a limited LOB size of less than 32 K is optimal when Oracle is your source database.

  • When a task is configured to run in limited LOB mode, the Max LOB size (K) option sets the maximum size LOB that AWS DMS accepts. Any LOBs that are larger than this value is truncated to this value.

  • When a task is configured to use full LOB mode, AWS DMS retrieves LOBs in pieces. The LOB chunk size (K) option determines the size of each piece. When setting this option, pay particular attention to the maximum packet size allowed by your network configuration. If the LOB chunk size exceeds your maximum allowed packet size, you might see disconnect errors. The recommended value for LobChunkSize is 64 kilobytes. Increasing the value for LobChunkSize above 64 kilobytes can cause task failures.

  • When a task is configured to run in inline LOB mode, the InlineLobMaxSize setting determines which LOBs DMS transfers inline.