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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1answer
1k 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 ...
2
votes
1answer
26 views

Implications of setting READ_Write

I am looking to update several users on READ_ONLY databases. As the databases are used 24/7 globally, and maintenance windows have just past, I would like to do this during a low-activity moment (to ...
0
votes
1answer
15 views

I have a DB that is locking up from numerous updates to a table: Should I convert it from MyISAM to InnoDB?

FYI: I don't believe this is a duplicate question, I've looked and most are general questions with vague answers. See more specifics below: Currently a database I am in charge of locks up every once ...
0
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0answers
17 views

Postgresql: Update or insert stuck

I'm running update-or-insert query on a table of approximatelly 3mln rows, 4 columns. Query is part of every day process, and for same days, the query stucks forever. It's just blocked. It's ...
2
votes
2answers
95 views

mysql write lock

I dont add any manual locking or any transaction anything, just manual running queries from php script, and execute below two update queries at the same time update table_x set status = 'PROCESSING' ...
0
votes
1answer
153 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 ...
0
votes
2answers
97 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 ...
2
votes
1answer
134 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
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0answers
46 views

MySQL: SELECT GET_LOCK slow/timeout

I am using "Zebra Session" as a replacement for PHP's built-in session management. Zebra Session stores sessions in a MySQL database, and uses "session locking" in order to ensure that data is ...
1
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1answer
50 views

Deadlock scenario, where is this S lock coming from?

I am encountering the below deadlock scenario. Please see the attached object definitions and execution plans. The plans were pulled out of cache from a system where this deadlock does occur. I ...
-1
votes
4answers
28k 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 ...
0
votes
1answer
434 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?
3
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1answer
55 views

How to perform server-side transaction timeout if COMMIT TRANSACTION will never arrive?

How can SQL Server terminate one of its transactions if it exceeds preset timeout? Imagine the following transaction performed by traveling salesman's SQL client application, which is submitted ...
0
votes
1answer
91 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 ( -- ...
1
vote
1answer
81 views

Work queue with complex select and long processing: Ensuring concurrency

I have a queue table from which worker processes claim records, one at a time. It is crucial that no two workers claim same item to process. Normally this kind of thing is done with select top (1) ...
1
vote
1answer
52 views

SELECT RELEASE_LOCK causing “Mysql has gone away”

During a long running process (90m+), our code calls SELECT RELEASE_LOCK('..');. However it always gives a "Mysql has gone away" error when we do this. We have tried a number of things including ...
2
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0answers
36 views

SQL Server 2008 R2 - Should I be worried at this statistics regarding indices causing locks?

We have some mild table locking issue during our peak hours so I figured the following query query taken from this site would be a good start. And boy, does it show me some seriously concerning ...
3
votes
4answers
6k 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
1answer
64 views

How to update a (very) large table without locking in MySQL

I have a large table (58+ million records) which represents a relation between two records (player and target) in a second table. Unfortunately, whoever designed our schema didn't think things ...
1
vote
2answers
78 views

Is it safe to cancel a PostgreSQL ALTER TABLE query that is waiting on a lock?

We started an ALTER TABLE query hours ago and only recently realized (via pg_stat_activity) that it is waiting on a lock. We discovered the other query that is holding a lock on the table we want to ...
3
votes
0answers
109 views

Slow transactions, many locks

At high load conditions the server app stops responding to client because begin/commit statements are executing very slowly (some take 15 seconds). The queries are simple - insert, update two columns ...
1
vote
1answer
61 views

What happens if two mySQL queries both try to lock the same row at the same time?

So this isn't exactly my strong suit, but here's my basic understanding of the situation: If two threads of the same application both try to execute the same query at the same time, mySQL will ...
2
votes
0answers
39 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
votes
1answer
61 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 ...
1
vote
2answers
118 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
33 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
votes
1answer
83 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
42 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
votes
2answers
142 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
votes
2answers
137 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 ...
2
votes
2answers
365 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
313 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
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0answers
204 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
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2answers
74 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
2k 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
67 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
74 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
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0answers
24 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
275 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
vote
1answer
155 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
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0answers
44 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
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0answers
21 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
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0answers
42 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
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1answer
168 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
45 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
90 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
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0answers
75 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 ...
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0answers
68 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 ...
8
votes
1answer
4k 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)); ...