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Does SQL Server's serializable isolation level lock entire table


What is lock escalation?How do I implement insert-if-not-found for transactions at serializable isolation level?MySQL InnoDB locks primary key on delete even in READ COMMITTEDDoes SQL Server place shared locks on scanned records when using REPEATABLE READWhy are U locks required when using Read Committed Snapshot IsolationSELECT INTO OUTFILE vs INSERT INTO … SELECTElevate transaction isolation in Maria DBUnderstanding repeatable read isolation levelWhy does this RX-X lock not appear in Extended Events?Key-range RangeI-N lock compatibility in SQL Server






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margin-bottom:0;









9


















Me and a colleague of mine discussed the implications of use of the serializable isolation level. He said it locked the entire table, but I disagreed to that telling him it potentially could but it tries to apply range locks and it doesn't apply true serialization as explained here: The Serializable Isolation Level.



I can't find anything in the docs either for the "locks entire table": SET TRANSACTION ISOLATION LEVEL.



The doc states a bunch of things regarding range locks, so in theory you could lock the entire table by simply having a range lock that locks the entire range of possible values in the table, but it doesn't lock the table.



Am I completely wrong here? Does it in fact lock the entire table (or tables)?










share|improve this question

































    9


















    Me and a colleague of mine discussed the implications of use of the serializable isolation level. He said it locked the entire table, but I disagreed to that telling him it potentially could but it tries to apply range locks and it doesn't apply true serialization as explained here: The Serializable Isolation Level.



    I can't find anything in the docs either for the "locks entire table": SET TRANSACTION ISOLATION LEVEL.



    The doc states a bunch of things regarding range locks, so in theory you could lock the entire table by simply having a range lock that locks the entire range of possible values in the table, but it doesn't lock the table.



    Am I completely wrong here? Does it in fact lock the entire table (or tables)?










    share|improve this question





























      9













      9









      9


      1






      Me and a colleague of mine discussed the implications of use of the serializable isolation level. He said it locked the entire table, but I disagreed to that telling him it potentially could but it tries to apply range locks and it doesn't apply true serialization as explained here: The Serializable Isolation Level.



      I can't find anything in the docs either for the "locks entire table": SET TRANSACTION ISOLATION LEVEL.



      The doc states a bunch of things regarding range locks, so in theory you could lock the entire table by simply having a range lock that locks the entire range of possible values in the table, but it doesn't lock the table.



      Am I completely wrong here? Does it in fact lock the entire table (or tables)?










      share|improve this question
















      Me and a colleague of mine discussed the implications of use of the serializable isolation level. He said it locked the entire table, but I disagreed to that telling him it potentially could but it tries to apply range locks and it doesn't apply true serialization as explained here: The Serializable Isolation Level.



      I can't find anything in the docs either for the "locks entire table": SET TRANSACTION ISOLATION LEVEL.



      The doc states a bunch of things regarding range locks, so in theory you could lock the entire table by simply having a range lock that locks the entire range of possible values in the table, but it doesn't lock the table.



      Am I completely wrong here? Does it in fact lock the entire table (or tables)?







      sql-server isolation-level serialization






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Sep 28 at 14:30









      Erik Darling

      29.6k13 gold badges89 silver badges146 bronze badges




      29.6k13 gold badges89 silver badges146 bronze badges










      asked Sep 28 at 6:57









      mslotmslot

      3055 bronze badges




      3055 bronze badges























          2 Answers
          2






          active

          oldest

          votes


















          16



















          Escalation, though



          Lock escalation under serializable isolation level may occur the same as it does with other isolation levels.



          • Correct indexes can help to avoid lock escalation up to a point

          • Locking many indexes will increase the likelihood of lock escalation; the count is cumulative across objects for a single statement

          Some quick examples using a single table with a single index. Id is the primary key and clustered index on the table.



          One Row



          SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
          BEGIN TRAN

          UPDATE c
          SET c.Score = 2147483647
          FROM dbo.Comments AS c
          WHERE c.Id = 138; --One value

          ROLLBACK


          For a single Id value, locking is minimal.



          +--------------+---------------+---------------+-------------+
          | request_mode | locked_object | resource_type | total_locks |
          +--------------+---------------+---------------+-------------+
          | RangeX-X | Comments | KEY | 1 |
          | IX | Comments | OBJECT | 1 |
          | IX | Comments | PAGE | 1 |
          +--------------+---------------+---------------+-------------+


          Multiple Rows



          But locks will go up if we start working in ranges:



          SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
          BEGIN TRAN

          UPDATE c
          SET c.Score = 2147483647
          FROM dbo.Comments AS c
          WHERE c.Id BETWEEN 1 AND 5000; -- Small range

          ROLLBACK


          Now we have more exclusive locks on more keys:



          +--------------+---------------+---------------+-------------+
          | request_mode | locked_object | resource_type | total_locks |
          +--------------+---------------+---------------+-------------+
          | RangeX-X | Comments | KEY | 2429 |
          | IX | Comments | OBJECT | 1 |
          | IX | Comments | PAGE | 97 |
          +--------------+---------------+---------------+-------------+


          Way More Rows



          This will carry on until we hit a tipping point:



          SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
          BEGIN TRAN

          UPDATE c
          SET c.Score = 2147483647
          FROM dbo.Comments AS c
          WHERE c.Id BETWEEN 1 AND 11655; --Larger range

          ROLLBACK


          Lock escalation is attempted and is successful:



          +--------------+---------------+---------------+-------------+
          | request_mode | locked_object | resource_type | total_locks |
          +--------------+---------------+---------------+-------------+
          | X | Comments | OBJECT | 1 |
          +--------------+---------------+---------------+-------------+


          Pay Attention



          It's important to separate two concepts here: the isolation level will be serializable no matter what kind of locks are taken. The query chooses the isolation level, and the storage engine chooses the locks. Serializable won't always result in range locks -- the storage engine can pick whichever kind of locks still honor the isolation level.






          share|improve this answer
































            5



















            If there is an index on a search predicate, it might be used for range locks.



            I.e., lock from first row to next in range. And from that next to third row, etc. Up to the last row in the range. So essentially a number of row locks, but it blocks the range from inserts also for "in-between" values (locking the range).



            For this to happen you (SQL Server) need to have an index to work with. Without indexes to do the locking in (indexes on predicates), you'll (from what I know) will get table locks.






            share|improve this answer




























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              2 Answers
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              2 Answers
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              active

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              16



















              Escalation, though



              Lock escalation under serializable isolation level may occur the same as it does with other isolation levels.



              • Correct indexes can help to avoid lock escalation up to a point

              • Locking many indexes will increase the likelihood of lock escalation; the count is cumulative across objects for a single statement

              Some quick examples using a single table with a single index. Id is the primary key and clustered index on the table.



              One Row



              SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
              BEGIN TRAN

              UPDATE c
              SET c.Score = 2147483647
              FROM dbo.Comments AS c
              WHERE c.Id = 138; --One value

              ROLLBACK


              For a single Id value, locking is minimal.



              +--------------+---------------+---------------+-------------+
              | request_mode | locked_object | resource_type | total_locks |
              +--------------+---------------+---------------+-------------+
              | RangeX-X | Comments | KEY | 1 |
              | IX | Comments | OBJECT | 1 |
              | IX | Comments | PAGE | 1 |
              +--------------+---------------+---------------+-------------+


              Multiple Rows



              But locks will go up if we start working in ranges:



              SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
              BEGIN TRAN

              UPDATE c
              SET c.Score = 2147483647
              FROM dbo.Comments AS c
              WHERE c.Id BETWEEN 1 AND 5000; -- Small range

              ROLLBACK


              Now we have more exclusive locks on more keys:



              +--------------+---------------+---------------+-------------+
              | request_mode | locked_object | resource_type | total_locks |
              +--------------+---------------+---------------+-------------+
              | RangeX-X | Comments | KEY | 2429 |
              | IX | Comments | OBJECT | 1 |
              | IX | Comments | PAGE | 97 |
              +--------------+---------------+---------------+-------------+


              Way More Rows



              This will carry on until we hit a tipping point:



              SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
              BEGIN TRAN

              UPDATE c
              SET c.Score = 2147483647
              FROM dbo.Comments AS c
              WHERE c.Id BETWEEN 1 AND 11655; --Larger range

              ROLLBACK


              Lock escalation is attempted and is successful:



              +--------------+---------------+---------------+-------------+
              | request_mode | locked_object | resource_type | total_locks |
              +--------------+---------------+---------------+-------------+
              | X | Comments | OBJECT | 1 |
              +--------------+---------------+---------------+-------------+


              Pay Attention



              It's important to separate two concepts here: the isolation level will be serializable no matter what kind of locks are taken. The query chooses the isolation level, and the storage engine chooses the locks. Serializable won't always result in range locks -- the storage engine can pick whichever kind of locks still honor the isolation level.






              share|improve this answer





























                16



















                Escalation, though



                Lock escalation under serializable isolation level may occur the same as it does with other isolation levels.



                • Correct indexes can help to avoid lock escalation up to a point

                • Locking many indexes will increase the likelihood of lock escalation; the count is cumulative across objects for a single statement

                Some quick examples using a single table with a single index. Id is the primary key and clustered index on the table.



                One Row



                SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                BEGIN TRAN

                UPDATE c
                SET c.Score = 2147483647
                FROM dbo.Comments AS c
                WHERE c.Id = 138; --One value

                ROLLBACK


                For a single Id value, locking is minimal.



                +--------------+---------------+---------------+-------------+
                | request_mode | locked_object | resource_type | total_locks |
                +--------------+---------------+---------------+-------------+
                | RangeX-X | Comments | KEY | 1 |
                | IX | Comments | OBJECT | 1 |
                | IX | Comments | PAGE | 1 |
                +--------------+---------------+---------------+-------------+


                Multiple Rows



                But locks will go up if we start working in ranges:



                SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                BEGIN TRAN

                UPDATE c
                SET c.Score = 2147483647
                FROM dbo.Comments AS c
                WHERE c.Id BETWEEN 1 AND 5000; -- Small range

                ROLLBACK


                Now we have more exclusive locks on more keys:



                +--------------+---------------+---------------+-------------+
                | request_mode | locked_object | resource_type | total_locks |
                +--------------+---------------+---------------+-------------+
                | RangeX-X | Comments | KEY | 2429 |
                | IX | Comments | OBJECT | 1 |
                | IX | Comments | PAGE | 97 |
                +--------------+---------------+---------------+-------------+


                Way More Rows



                This will carry on until we hit a tipping point:



                SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                BEGIN TRAN

                UPDATE c
                SET c.Score = 2147483647
                FROM dbo.Comments AS c
                WHERE c.Id BETWEEN 1 AND 11655; --Larger range

                ROLLBACK


                Lock escalation is attempted and is successful:



                +--------------+---------------+---------------+-------------+
                | request_mode | locked_object | resource_type | total_locks |
                +--------------+---------------+---------------+-------------+
                | X | Comments | OBJECT | 1 |
                +--------------+---------------+---------------+-------------+


                Pay Attention



                It's important to separate two concepts here: the isolation level will be serializable no matter what kind of locks are taken. The query chooses the isolation level, and the storage engine chooses the locks. Serializable won't always result in range locks -- the storage engine can pick whichever kind of locks still honor the isolation level.






                share|improve this answer



























                  16















                  16











                  16









                  Escalation, though



                  Lock escalation under serializable isolation level may occur the same as it does with other isolation levels.



                  • Correct indexes can help to avoid lock escalation up to a point

                  • Locking many indexes will increase the likelihood of lock escalation; the count is cumulative across objects for a single statement

                  Some quick examples using a single table with a single index. Id is the primary key and clustered index on the table.



                  One Row



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id = 138; --One value

                  ROLLBACK


                  For a single Id value, locking is minimal.



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | RangeX-X | Comments | KEY | 1 |
                  | IX | Comments | OBJECT | 1 |
                  | IX | Comments | PAGE | 1 |
                  +--------------+---------------+---------------+-------------+


                  Multiple Rows



                  But locks will go up if we start working in ranges:



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id BETWEEN 1 AND 5000; -- Small range

                  ROLLBACK


                  Now we have more exclusive locks on more keys:



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | RangeX-X | Comments | KEY | 2429 |
                  | IX | Comments | OBJECT | 1 |
                  | IX | Comments | PAGE | 97 |
                  +--------------+---------------+---------------+-------------+


                  Way More Rows



                  This will carry on until we hit a tipping point:



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id BETWEEN 1 AND 11655; --Larger range

                  ROLLBACK


                  Lock escalation is attempted and is successful:



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | X | Comments | OBJECT | 1 |
                  +--------------+---------------+---------------+-------------+


                  Pay Attention



                  It's important to separate two concepts here: the isolation level will be serializable no matter what kind of locks are taken. The query chooses the isolation level, and the storage engine chooses the locks. Serializable won't always result in range locks -- the storage engine can pick whichever kind of locks still honor the isolation level.






                  share|improve this answer














                  Escalation, though



                  Lock escalation under serializable isolation level may occur the same as it does with other isolation levels.



                  • Correct indexes can help to avoid lock escalation up to a point

                  • Locking many indexes will increase the likelihood of lock escalation; the count is cumulative across objects for a single statement

                  Some quick examples using a single table with a single index. Id is the primary key and clustered index on the table.



                  One Row



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id = 138; --One value

                  ROLLBACK


                  For a single Id value, locking is minimal.



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | RangeX-X | Comments | KEY | 1 |
                  | IX | Comments | OBJECT | 1 |
                  | IX | Comments | PAGE | 1 |
                  +--------------+---------------+---------------+-------------+


                  Multiple Rows



                  But locks will go up if we start working in ranges:



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id BETWEEN 1 AND 5000; -- Small range

                  ROLLBACK


                  Now we have more exclusive locks on more keys:



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | RangeX-X | Comments | KEY | 2429 |
                  | IX | Comments | OBJECT | 1 |
                  | IX | Comments | PAGE | 97 |
                  +--------------+---------------+---------------+-------------+


                  Way More Rows



                  This will carry on until we hit a tipping point:



                  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
                  BEGIN TRAN

                  UPDATE c
                  SET c.Score = 2147483647
                  FROM dbo.Comments AS c
                  WHERE c.Id BETWEEN 1 AND 11655; --Larger range

                  ROLLBACK


                  Lock escalation is attempted and is successful:



                  +--------------+---------------+---------------+-------------+
                  | request_mode | locked_object | resource_type | total_locks |
                  +--------------+---------------+---------------+-------------+
                  | X | Comments | OBJECT | 1 |
                  +--------------+---------------+---------------+-------------+


                  Pay Attention



                  It's important to separate two concepts here: the isolation level will be serializable no matter what kind of locks are taken. The query chooses the isolation level, and the storage engine chooses the locks. Serializable won't always result in range locks -- the storage engine can pick whichever kind of locks still honor the isolation level.







                  share|improve this answer













                  share|improve this answer




                  share|improve this answer










                  answered Sep 28 at 13:01









                  Erik DarlingErik Darling

                  29.6k13 gold badges89 silver badges146 bronze badges




                  29.6k13 gold badges89 silver badges146 bronze badges


























                      5



















                      If there is an index on a search predicate, it might be used for range locks.



                      I.e., lock from first row to next in range. And from that next to third row, etc. Up to the last row in the range. So essentially a number of row locks, but it blocks the range from inserts also for "in-between" values (locking the range).



                      For this to happen you (SQL Server) need to have an index to work with. Without indexes to do the locking in (indexes on predicates), you'll (from what I know) will get table locks.






                      share|improve this answer































                        5



















                        If there is an index on a search predicate, it might be used for range locks.



                        I.e., lock from first row to next in range. And from that next to third row, etc. Up to the last row in the range. So essentially a number of row locks, but it blocks the range from inserts also for "in-between" values (locking the range).



                        For this to happen you (SQL Server) need to have an index to work with. Without indexes to do the locking in (indexes on predicates), you'll (from what I know) will get table locks.






                        share|improve this answer





























                          5















                          5











                          5









                          If there is an index on a search predicate, it might be used for range locks.



                          I.e., lock from first row to next in range. And from that next to third row, etc. Up to the last row in the range. So essentially a number of row locks, but it blocks the range from inserts also for "in-between" values (locking the range).



                          For this to happen you (SQL Server) need to have an index to work with. Without indexes to do the locking in (indexes on predicates), you'll (from what I know) will get table locks.






                          share|improve this answer
















                          If there is an index on a search predicate, it might be used for range locks.



                          I.e., lock from first row to next in range. And from that next to third row, etc. Up to the last row in the range. So essentially a number of row locks, but it blocks the range from inserts also for "in-between" values (locking the range).



                          For this to happen you (SQL Server) need to have an index to work with. Without indexes to do the locking in (indexes on predicates), you'll (from what I know) will get table locks.







                          share|improve this answer















                          share|improve this answer




                          share|improve this answer








                          edited Sep 29 at 18:28









                          Razvan Socol

                          1927 bronze badges




                          1927 bronze badges










                          answered Sep 28 at 11:08









                          Tibor KarasziTibor Karaszi

                          2,9201 silver badge9 bronze badges




                          2,9201 silver badge9 bronze badges































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