A mechanism for managing concurrent access to shared data or resources by granting temporarily exclusive access to the processes requesting the lock.

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2
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0answers
27 views

When does SQL Server acquire locks?

The list of isolation levels in SQL Server found here states that write locks acquired within a transaction are retained until the end of the transaction. However it doesn't mention anything about ...
3
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1answer
30 views

(How) does table inheritance interfere with locking in postgres?

I have a table inheritance setup that might be simplified like this: CREATE TABLE p ( id BIGSERIAL PRIMARY KEY, type_id BIGINT, approved BOOLEAN ); CREATE INDEX ON p(approved); CREATE ...
2
votes
1answer
965 views

Insert into table from a query to a linked database hangs

I have a schema with some database links to other schemas that we use to pull data from. We pull the data into a staging table, massage it, and then do some merges into our schema/database. The data ...
1
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2answers
97 views

SQL Server - Slow Database for no apparent reason [closed]

I have a DB Server running SQL Server 2008 R2 SP2 on 24 physical Cores and 32GB of RAM. The database files are on a SSD Raid1 and the TempDB on a SAS 15k (150GB DB) I assume that the server has more ...
1
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0answers
26 views

Average Waiter Count increasing

I am in a nightmare. We have deployed an application to a UAT environment, which has only 7 users. Since then, we have noticed in the logs, a lot of deadlocks, and processes being victims and things. ...
3
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1answer
69 views

enabling snapshot isolation level on a database - what to monitor?

I am having problems with frequent deadlocks on a subscription database. I am considering enabling the snapshot isolation level for that database. I am aware that there is an overhead on the tempDb ...
25
votes
4answers
2k views

Is NOLOCK always bad?

I am a Report Developer who wants to make my queries as efficient as possible. I used to work with a DBA who told me - I believe because I was always dealing with reports on a Production Server - to ...
0
votes
1answer
29 views

GET_LOCK([name], 0) behaviour and multiple GET_LOCK() order

I read from the documentation that the behavior of distributing a lock requested by many connections after RELEASE_LOCK is called from the connection holding the lock is undefined. I was curious: say ...
10
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2answers
125 views

SQL Server Index Update Deadlock

I have 2 queries which when run at the same time are causing a deadlock. Query 1 - update a column which is included in an index (index1): update table1 set column1 = value1 where id = @Id Takes ...
0
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1answer
91 views

MySQL 5.6 replication causes 'waiting for table lock'

All of the sudden queries on slave server stopped with status "Waiting for table level lock" I restart mysql service and stop replications and locking does not show up anymore. Once I turn ...
2
votes
1answer
84 views

How mysql (innodb) handles auto increment column

I am working on a OLTP environment with multiple parallel write operation. I found this in documentation about auto increment locking but still i am interested to know much about it in details. Can ...
0
votes
1answer
237 views

How to generate replication snapshot without locking tables

When I reinitialize subscription and generate new snapshot it locks all tables and makes the database unusable for a very long time (never waited it out). Is there anyway to do this without locking?
0
votes
2answers
102 views

Determine whether there is any blocking while deleting large number of records [closed]

I would like to know whether there is any way to determine why it is taking too much time say 3 minutes for deleting 50K records from a database hosted in Sql Azure. I have clustered index on primary ...
0
votes
0answers
47 views

Concurrent SELECT and UPDATE in multiprocessing python

I have to randomly match about 20 million rows in two tables without using the same row twice using PostgreSQL 9.3.5. Both tables have the following structure CREATE TABLE de_sim_points_end ( -- ...
2
votes
2answers
106 views

When is it safe to disable InnoDB doublewrite buffering?

MySQL InnoDB allows us to disable doublewrite buffering by setting innodb_doublewrite = 0. Other databases doesn't seem to allow this setting to be tweaked. How could InnoDB still be able to maintain ...
5
votes
1answer
245 views

SELECT INTO OUTFILE vs INSERT INTO … SELECT

During my cursory research I have not been able to find a definitive answer on the benefits that SELECT INTO OUTFILE provides over INSERT INTO ... SELECT. Upon reading the docs related to INSERT INTO ...
0
votes
0answers
73 views

Many transactions are getting stuck in the “cleaning up” state - what could cause that?

I'm trying to track down a locking issue, and found via SHOW PROCESSLIST that when the queries in question are waiting for locks and timing out, there are no other queries active in the process list. ...
0
votes
2answers
48 views

Alter table statement waiting (for hours, on dev machine), but no locks shown

I have been trying to issue a simple: ALTER TABLE tablename ADD COLUMN id_col character varying (30) type statement on a Postgres 9.1.13 build on Debian. The application is still in private beta, so ...
0
votes
2answers
1k views

How can I find who has allocated a user lock via dbms_lock?

We have a print queue process that acquires a user lock via dbms_lock.allocate_unique. It performs the work and then releases the lock. The process works very well. Today, we have a process that ...
0
votes
1answer
27 views

Sybase ASE lock table to disallow users insert values

I need to disallow users to insert values in some table, for example for a 5 mins. Seems I should use at isolation clause but can't figure out how to use it. Thanks
3
votes
1answer
52 views

InnoDB & Isolation Levels - Aren't repeatable reads a bad thing?

I was reading about InnoDB's isolation levels and it makes sense for the most part, but what I don't get is why are unrepeatable reads a bad thing? Shouldn't it be the other way around? For examples: ...
0
votes
0answers
20 views

MySQL what is the order of the table lock for this query?

An example query looks like this: INSERT INTO Adventure (sword, fighter, quest) SELECT Swords.id, Fighters.id, Quests.id FROM swords Swords, fighters Fighters, quests Quests WHERE Swords._id = ...
6
votes
2answers
226 views

Is this update, select combination query thread safe?

I have a table called seats, which has a schema like this id,taken For each user, I take a random untaken id and assign to that user, here for simplicity say, I make taken =1. The query I am ...
1
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1answer
113 views

How many rows will be locked by SELECT … ORDER BY xxx LIMIT 1 FOR UPDATE?

As was asked on stackoverflow but then for MySQL, I was wondering how this works in PostgreSQL. How many rows get locked when I do a "FOR UPDATE" in combination with a "LIMIT", a "ORDER BY" and some ...
1
vote
0answers
29 views

Handling this multi-threading scenario in the database?

I am working on sample bus ticket booking application,in I am facing these two multi-threading scenarios. Scenario 1 1: Let's say there are two users, they both pick a particular seat and submit ...
1
vote
0answers
20 views

MySQL - Transactions and causality

I'm new to MySQL's LOCK and TRANSACTION and have a question about different isolation levels of a transaction: Given two transactions executing the same code (auto-commit is false): (1) get data of ...
0
votes
0answers
34 views

SSRS 2012 LCK_M_IX locks

I have an SSRS server running in native mode. Sometimes i see in sys.dm_exec_requests a lot of locks LCK_M_IX, which occurs while system procedures(like WriteChunkSegment, ReadChunkSegment) are ...
0
votes
2answers
63 views

One of databases in MongoDB suddenly gets high lock %

I observe repeatable, sudden, short-time update queries slowdowns in MongoDB cluster for single database. That slowdowns lasts about 30 seconds and repeats few times a day. I found that lock % and ...
0
votes
1answer
75 views

What does it mean when I see a lock in sys.dm_tran_locks and there's no matching row in sys.dm_exec_requests?

I'm running this query select sessions.session_id from sys.dm_tran_locks locks inner join sys.dm_exec_sessions sessions on locks.request_session_id=sessions.session_id and it consistently ...
0
votes
0answers
39 views

How can I obtain concurrent deletes for this table?

We have a program that is currently doing something to the effect of: SET TRANSACTION ISOLATION LEVEL READ COMMITTED BEGIN TRANSACTION UPDATE [Source].[dbo].[SourceTable] SET [ProcessedOn] = ...
1
vote
1answer
72 views

Why would I not specify ROWLOCK to get rid of page locks?

I have a query that goes something like this: SELECT TOP (1) * FROM MyTable WITH (UPDLOCK, READPAST) ORDER BY SomeColumn ASC; This answer says that it's hard to say for sure but it will probably ...
0
votes
0answers
62 views

MySQL Upgrade from 5.5 to 5.6 causes system / table locks

We recently upgraded from MySQL 5.5 to 5.6 on AWS RDS. Before, we had a relatively performant database - definitely had its quirks, but it seemed to be tuned relatively well. After the upgrade, we're ...
-1
votes
2answers
19k views

How to determine if an Oracle table is locked or not?

We've been using BI software and a repository database that are installed on Oracle Enterprise 11gR2. Some of these batch reports will try to access a database table which may still be locked. How ...
1
vote
0answers
41 views

Postgres advisory lock deadlocks itself?

I am executing pg_advisory_locks using the following set of statements: SELECT pg_advisory_lock(317,2); UPDATE posts SET dislikers = array_remove(dislikers, 7) WHERE id = 317; update posts set ...
7
votes
1answer
1k views

Detecting the locked table or row in SQL Server

I'm trying to understand/learn how to track down the details of a blocked session. So I created the following setup: create table foo (id integer not null primary key, some_data varchar(20)); ...
0
votes
1answer
86 views

READ_COMMITTED_SNAPSHOT locking on Non-Clustered Index

I'm in big trouble with one database instance of SQL Server 2008 R2. I have this structure that I've created it to simulate my real problem: USE [sor] GO ALTER DATABASE [sor] SET ...
11
votes
3answers
737 views

Will increased network latency cause table locks in MS SQL Server?

If I'm making a single call to a SQL Server database over a high-latency network, will table locks occur due to that latency? Say I query table A for some records, and SQL Server has to return that ...
0
votes
1answer
520 views

InnoDB row level locks without SELECTs?

I have several (>30) MySQL clients inserting into InnoDB tables concurrently. I keep encountering lock wait timeouts and can't figure out why. Here is the situation: Each client runs the following ...
4
votes
1answer
311 views

Optimizing concurrent updates in Postgres

I'm running concurrent Postgres queries like this: UPDATE foo SET bar = bar + 1 WHERE baz = 1234 Each query affects the fixed K number of rows, and I can't find a way to enforce the order in which ...
1
vote
1answer
33 views

What happens when you have two events scheduled to run after identical n seconds?

I am running a survey and i am getting lots of data and i need to process that data quickly from within mysql.I am using a mysql events to help me process the hundreds of rows that i have. I have ...
1
vote
1answer
40 views

Is it possible that records are changed while a read query is still executing?

Suppose a read (select) query R is reading some 100 records from a table, 50 records are read so far, could in the meanwhile a write query W change some of the unread records? We didn't take any ...
2
votes
1answer
1k views

What could cause waiting for table metadata lock?

I am using a MySQL 5.6 DB with MyISAM tables under FreeBSD 8.3. The main part of code is in PHP, but the problem arises, when I launch the self-written on C++ chat-server. I use the mysql.h for DB ...
3
votes
4answers
5k views

Why is optimistic locking faster than pessimistic locking?

Both forms of locking cause a process to wait for a correct copy of the record if its currently in use by another process. With pessimistic locking, the lock mechanism comes from the DB itself (a ...
0
votes
3answers
120 views

postgresql cannot drop a table when autovacuum holds lock on it

Autovacuuming process holds RowExclusiveLock and ShareUpdateExclusiveLock on the table, which I want to drop. I read that autovacuum should be canceled automatically, when submitting DROP TABLE ...
0
votes
0answers
75 views

Unresponsive MySQL database

I've setup a MySQL server on Ubuntu machine. When running a heavy query (the table has over 1M rows), the database becomes unresponsive. Upon connection it returns: Can't connect to MySQL server ...
10
votes
1answer
390 views

Sch-M WAIT blocks Sch-S in SQL Server 2014 but not SQL Server 2008 R2?

We recently migrated our production instances from SQL 2008 R2 to brand new SQL 2014 servers. Here is an interesting scenario that we uncovered with our usage of Service Broker. Consider a database ...
1
vote
1answer
186 views

MySQL consistent nonlocking reads vs. INSERT … SELECT

So, from my reading of the MySQL 5.5 documentation and some experiments I did with colleagues, I understand that the following is the case: With InnoDB tables, a simple SELECT statement (one that ...
1
vote
0answers
79 views

Update on a small table times out

We use Microsoft SQL Server Express Edition with Advanced Services 2008 R2 SP2 We have two locations. Each location has one sql server that serves about 20 client computers. Client computers are ...
4
votes
2answers
1k views

Why did my UPDATE statement not complete?

Running SQL Server 2008; Mgmt Studio 2008. I am working with a MS SQL job that we have created for our MS CRM 4.0 implementation. For anyone familiar with CRM, this job purges the aSyncOperationBase ...
1
vote
1answer
121 views

Improve performance on concurrent UPDATEs for a timestamp column in Postgres

I am using a timestamp column called updated_at for cache invalidation. More information on this particular technique here. The queries all have the same format UPDATE "managers" SET "updated_at" = ...