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What is page locking

Posted on 1998-12-14
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Last Modified: 2010-07-27
What is page locking in SQL and how large is a page?
Has a page a fix size e.g. 4KB or 8KB or a number of records?
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Question by:flmexpert
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Victor Spiridonov earned 0 total points
ID: 1092277
Page locking is like putting a flag on the page. The flag, depending on lock can mean: 'Don't allow any one to access this page' (in case of update lock) or for example, 'Allow to read, but don't allow to update' (in case of shared select lock). There are several lock types, that can be placed on a page,you can read about them in SQL Books Online. Page size in Sql Server is 2Kb.
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by:tschill120198
ID: 1092278
SQL 7.0 increases the page size to 8K.
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by:flmexpert
ID: 1092279
SQL 7.0 uses record locking and why should it use also pages ?

Also there is a problem:
If i have a record with a size of 3 KB and
make "update ... where <this record>".
SQL 7 locks only this record and SQL 6.5 ?
Locks it this record with two 2 KB pages ?

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by:tschill120198
ID: 1092280
This is called "lock escalation", where SQL converts many fine-grain locks into fewer course-grain locks to reduce the overhead of managing the locks...  

Resources that it can lock (from smaller to larger granularity) are: RID -> Key -> Page -> Extent -> Table -> Database.

Look in BOL under "lock escalation".

As for the update query locking 2 pages, since the record is 3K (and therefore resides on 2 pages), it would make sense that both pages for the record be locked.  Or am I missing something?

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