Hi @sakuraime ,
The ESTIMATEONLY option calculates how much space might be required in tempdb for the sort that holds the facts generated by the consistency-checking algorithms, taking into account all other specified options. DBCC CHECKDB goes through the motions of building all the batches of objects to check, but it doesn’t actually check them. Instead, it uses the metadata that it has gathered about each table and index to produce an estimate of the number of each type of fact that it generates. The various numbers are multiplied by the size of each fact type and added together to form a total size for that batch. The batch with the highest total size is the one that’s reported. The estimation algorithms are very conservative in their calculations to ensure that an accurate maximum size is returned. The actual amount of tempdb space taken up might be considerably lower. For example, the estimation algorithm estimates the number of facts required to track forwarding and forwarded records by simply counting all the records in a heap and multiplying by two. This is almost never the case, but it is a sufficient estimation.
And also, please refer to How does DBCC CHECKDB WITH ESTIMATEONLY work? to get more information. Hope this will help you, if there has any other questions, please let me know. Thank you.
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