Press "Enter" to skip to content

The Mechanisms of Page Splits

Deepthi Gogrui takes us through page splitting in SQL Server:

Page splits can happen with the logical fragmentation and low page density causing the transactional log to be huge. Page splits are very expensive. As we learned from the previous post, page splits happens when SQL Server tries to insert a row and there is no more space on the page to fit in the page so page will split the page to give the space to fit it in that record. When SQL Server has to insert any rows in to the pages, first the free space on the page is checked at the header information of the page and if the record is within the mentioned free bytes, the record fits in. If the space is not contiguous within the page but there is total space to fit in the record, then the in-memory compaction of the page making the amount of free space on the page contiguous. This is not page split. Page split occurs when the space is not available on the page to fit in the record, in that case page split into half and the split point of the page is usually 50 percent each. Sometimes, the split can happen at the different point on the page is chosen by the storage engine as the obvious split point which is known as skewed page split. This is even more expensive when compared with the regular page split as this will create much larger transaction log.

What causes the page splits?

Read on for the full article.