Describe 首頁/2020-12-07 here.
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This may also be due to a few other factors, for example: - Encryption of data (either in Oracle or during backup) - encrypted data does not de-duplicate well as every time a small piece of data changes the entire chunk of encrypted data appears to change (due to the encryption algorithm). When using encryption you should normally expect low de-duplication ratio but reasonable local compression ratio - Compression of data (again either in Oracle or during backup) - as with encrypted data even if a small piece of data within the database changes the entire chunk of data which is compressed together appears to change (due to the compression algorithm). As a result compressed data normally gives poor de-duplication AND compression ratios - Use of binary data embedded within tables - binary data such as image/media files tends to be pre-compressed by its codec so is essentially compressed data and all of the points above apply - Backing up archive logs - archive logs contain transactional data which tends to be very unique from backup to backup - as a result de-duplication ratio for archive log backups is generally very poor however these should still compress (if not compressed during the backup) - Very high change rate within your databases - if the majority of the data changes between backups then most of each backup will appear to be 'new' data which the DDR has not seen before. As a result it does not de-duplicate well (however should still compress if not compressed during the backup) Hopefully that helps a little. 这也可能是由于其他一些因素引起的，例如： -数据加密（在Oracle中或在备份过程中）-加密的数据不能很好地重复数据删除，因为每当一小块数据更改时，整个加密数据块都似乎发生了更改（由于加密算法）。使用加密时，通常应该期望低重复数据删除率，但合理的本地压缩率 -数据压缩（再次在Oracle中或在备份过程中）-与加密数据一样，即使数据库中的一小块数据改变了，压缩在一起的整个数据块也似乎发生了变化（由于压缩算法）。结果，压缩数据通常会导致重复数据删除和压缩率不佳 -使用嵌入在表中的二进制数据-诸如图像/媒体文件之类的二进制数据倾向于通过其编解码器进行预压缩，因此本质上是压缩数据，并且上述所有要点都适用 -备份存档日志-存档日志包含的事务数据在备份到备份之间往往是非常独特的-因此，存档日志备份的重复数据删除率通常很差，但是仍应压缩（如果在备份期间未压缩） -数据库中的更改率非常高-如果大多数数据在两次备份之间发生更改，则每个备份中的大多数将显示为DDR之前从未见过的“新”数据。结果，它不能很好地重复数据删除（但是，如果在备份过程中未压缩，则仍应压缩）