Shared - Locks in SQL Server - Part 3
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Shared (S) locks allow concurrent transactions to read (SELECT) a resource under pessimistic concurrency control. No other transactions can modify the data while shared (S) locks exist on the resource. Shared (S) locks on a resource are released as soon as the read operation completes, unless the transaction isolation level is set to repeatable read or higher, or a locking hint is used to retain the shared (S) locks for the duration of the transaction.
Isolation Level - • SQL Server Isolation Example
Script for Active_Locks Function
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Create Function Active_locks () returns table return
select Top 10000000 case dtl.request_session_id
when -2 then 'orphaned distributed transaction'
when -3 then 'deferred recovery transaction'
else dtl.request_session_id end as spid,
db_name(dtl.resource_database_id) as databasename,
so.name as lockedobjectname, dtl.resource_type as lockedresource,
dtl.request_mode as locktype, es.login_name as loginname, es.host_name as hostname,
case tst.is_user_transaction when 0 then 'system transaction'
when 1 then 'user transaction' end as user_or_system_transaction,
at.name as transactionname, dtl.request_status
from sys.dm_tran_locks dtl join sys.partitions sp on sp.hobt_id = dtl.resource_associated_entity_id
join sys.objects so on so.object_id = sp.object_id
join sys.dm_exec_sessions es on es.session_id = dtl.request_session_id
join sys.dm_tran_session_transactions tst on es.session_id = tst.session_id
join sys.dm_tran_active_transactions at on tst.transaction_id = at.transaction_id
join sys.dm_exec_connections ec on ec.session_id = es.session_id
cross apply sys.dm_exec_sql_text(ec.most_recent_sql_handle) as st
where resource_database_id = db_id() order by dtl.request_session_id
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