These examples will be covered SQL Server Locking basic

1. IF EXISTS( SELECT 1
FROM sys.views
WHERE name = 'DBlocks')
DROP VIEWDBlocks;
GO
CREATE VIEW DBlocksAS
SELECT request_session_idASspid,
DB_NAME(resource_database_id) ASdbname ,
CASEWHEN resource_type ='OBJECT'
THEN OBJECT_NAME(resource_associated_entity_id)
WHEN resource_associated_entity_id=0 THEN 'n/a'
ELSE OBJECT_NAME(p.object_id)
END ASentity_name ,
index_id,
resource_type ASresource ,
resource_descriptionASdescription,
request_modeASmode ,
request_statusASstatus
FROM sys.dm_tran_lockst
LEFT JOIN sys.partitionsp
ON p.partition_id=t.resource_associated_entity_id
WHERE resource_database_id=DB_ID()
ANDresource_type <>'DATABASE' ;
GO

2. -- Example 1: SELECT withREAD COMMITTED
-- isolationlevel
USE General;
SET TRANSACTION ISOLATION LEVELREADCOMMITTED ;
BEGIN TRAN
SELECT *
FROM dbo.GenderNG
WHERE gendername ='Reflector';
SELECT *
FROM DBlocks
WHERE spid= @@spid;
COMMIT TRAN
/*There are nolockson the data in the Production.Producttable because the batch
was doingonlySELECT operations,andsoacquiredonlySlocks.By default,SQLServer
releasesSlocksassoon as ithas finishedreadingthe dataso,by the time we execute
the SELECT fromthe view,SQLServerno longerholdsthe locks.
*/
-- Example 2: SELECT withREPEATABLE READ
-- isolationlevel

3. USE General ;
SET TRANSACTION ISOLATION LEVELREPEATABLEREAD ;
BEGIN TRAN
SELECT gendername,sex
FROM dbo.GenderNG
WHERE gendername LIKE'Ana%';
SELECT *
FROM DBlocks
WHERE spid= @@spid
ANDentity_name ='GenderNG';
COMMIT TRAN
/*
Thistime,because the transactionisolationlevelisREPEATABLEREAD,SQL Serverholds
the S locksuntil the transactionisfinishedandsowe can see theminour results.The
dbo.GenderNGtable hasaclusteredindex,sothe rowsof data are all index rows
inthe leaf level.Assuch,the locksonthe 19 individual datarows
returnedare KEY locks.The table alsohas a non-clusteredindexonthe genderNamecolumn
and we can see 19 KEY locksat the leaf level of thisnon-clusteredindex,usedtofindthe
relevantrows.
*/
-- Example 3: SELECT withSERIALIZABLEisolation
-- level

4. USE General ;
SET TRANSACTION ISOLATION LEVELSERIALIZABLE;
BEGIN TRAN
SELECT *
FROM dbo.GenderNG
WHERE gendername LIKE'Ana%';
SELECT *
FROM DBlocks
WHERE spid= @@spid
ANDentity_name ='GenderNG';
COMMIT TRAN
/*
The two-partmode RangeS-Sindicatesakey-range lockinadditiontothe lockon the
keyitself.The firstpart(RangeS) isthe lockonthe range of keysbetweenandincluding
the keyholdingthe lockandthe previouskeyinthe index.The key-rangelocksprevent
othertransactionsfrominsertinganynew rowsintothe table thatmeetthe conditionof
thisquery;that is,it'snot possible toinsertanynew rowswithaproduct name starting
withRacingSocks.The key-range locksare heldonrangesinthe non-clusteredindex
on gendername (Index_id=3) because thatisthe index usedto findthe qualifyingrows.
*/
-- Example 4: Update withREAD COMMITTED
-- isolationlevel

5. USE General ;
SET TRANSACTION ISOLATION LEVELREADCOMMITTED ;
BEGIN TRAN
UPDATE dbo.GenderNG
SET Sex = 1
WHERE gendername LIKE'Adam%';
SELECT *
FROM DBlocks
WHERE spid= @@spid
ANDentity_name ='GenderNG';
COMMIT TRAN
/*
the two rowsinthe leaf level of the clusteredindex are lockedwith
X locks.The page and the table are thenlockedwithIXlocks.
As discussedearlier,SQLServeracquiresUlockswhile itlooksforthe rowsto update.
However,SQLServerescalatesthese toXlocksuponperformingthe actual update and,
by the time we lookat the DBlocksview,the U locksare gone.Unlesswe force U locks
witha queryhint,we mightneversee theminthe lockreportfromDBlocks,or by direct
inspectionof sys.dm_tran_locks.
*/
-- Example 5: Update withSERIALIZABLEisolation
-- level (withanindex)

6. USE General ;
SET TRANSACTION ISOLATION LEVELSERIALIZABLE
BEGIN TRAN
UPDATE dbo.GenderNG
SET Sex = 1
WHERE gendername LIKE'Adam%';
SELECT *
FROM DBlocks
WHERE spid= @@spid
ANDentity_name ='GenderNG';
COMMIT TRAN
/*
Again,notice thatthe key-range locksare onthe non-clusteredindex,usedtofindthe
relevantrows.The range interval itself needsonlyanSlockto preventinsertions,but
the searchedkeyshave U locks,ensuringthatnootherprocesscan attempttoUPDATE
them.The keysinthe table itself (index_id= 1) obtainthe X lockwhenthe actual
modificationismade.
*/
-- Example 6: Update withSERIALIZABLEisolation
-- level notusinganindex
USE General ;
SET TRANSACTION ISOLATION LEVELSERIALIZABLE

7. BEGIN TRAN
UPDATE dbo.GenderNG
SET Sex = 1
WHERE Sex = 2 ;
SELECT *
FROM DBlocks
WHERE spid= @@spid
ANDentity_name ='GenderNG';
COMMIT TRAN
/*
As there wasno useful index,aclusteredindexscanonthe entire table wasrequired,
and so all keysinitiallyreceivedthe RangeS-Ulock;whenfourrowswere eventually
modified,the locksonthose keysescalatedtothe RangeX-Xlock.We cansee twoof
the RangeX-Xlocks,anda fewof the RangeS-Ulocks.The complete outputhas501
RangeS-Ulocks,as well asIU lockson several pages,IXlocksontwopages,and an IX
lockon the table.
*/
-- Example 7: Creatinga table
USE General ;
SET TRANSACTION ISOLATION LEVELREADCOMMITTED ;
BEGIN TRAN
SELECT *

8. INTO newGender
FROM dbo.GenderNG
WHERE Sex BETWEEN 1 AND 2 ;
SELECT *
FROM DBlocks
WHERE spid= @@spid;
COMMIT TRAN
/*
SQL Serveracquiredveryfewof these locksonelementsof the
newGendertable.Inthe entity_name column,note thatmostof the objectsare
undocumented, andnormallyinvisible,systemtable names.Whencreatingthe new table,
SQL Serveracquireslocksonsix differentsystemtablestorecordinformationabout
thisnewtable.Inaddition,notice the schemamodification(Sch-M) locks
*/
-- Example 8: RID locks
USE General ;
SET TRANSACTION ISOLATION LEVELREADCOMMITTED
BEGIN TRAN
UPDATE newGender
SET Sex = 1
WHERE genderName ='Alan';
SELECT *
FROM DBlocks

9. WHERE spid= @@spid
ANDentity_name ='newGender';
COMMIT TRAN
/*
There are noindexesonthe newProductstable,sothe lockonthe actual row meeting
our criterionisan Xlock on the row(RID).For RID locks,the descriptionactuallyreports
the specificrowinthe form File Number:Page number:Slotnumber.Asexpected,SQL
ServertakesIXlockson the page and the table.
*/