I've executed the copy table operation from PhpMyAdmin and it is taking too long (big table), and now the original and new table are not responding (I can browse the other tables in PhpMyAdmin)
I think because maybe there is a read lock or something worst, is possible to cancel the operation or see at least what's happening?
Two possible things - first, you could restart the webserver to stop any running PHP scripts. That might help if PHPMyAdmin copies the data in batches.
Second, you can execute show full processlist query to see all running queries. Identifying the hung query should not be too hard. Then use kill <pid> query (replace the with the actual process ID) to kill that query.
On phpMyAdmin's main page, go to Status > Processes. You should be seeing one process with a large value under Time; use the Kill link to stop it.
If I try to run queries (even as easy as select id from table limit 1 ) on some specific tables in a schema (only a few of them have this problem) I get stuck.
When looking at the processlist, the state is "Waiting for table flush".
Any suggestion about how do I unlock these tables so that I can query them?
Pileups of queries stuck in "Waiting for table flush" state are typically caused by something in the background excessively running "FLUSH TABLES" or ANALYZE TABLE statements. Most backup methods need to do this briefly when they begin, but if you are getting it all the time, the chances are that you have a process or a cron job somewhere doing this excessively. Find the source of this and disable it, and the problem should go away.
For MySQL
Identify the processes causing issues.
This command will help to detect processes waiting for disk I/O in D state:
watch "ps -eo pid,user,state,command | awk '\$3 == /D/ { print \$0 }'"
You can also seek processes with long runtime like this:
SHOW FULL PROCESSLIST\G
Fix the processes or related queries you previously detected.
If you need to kill the detected processes, you can find their ids with the previous full processlist and execute the command: KILL <pid>;
In case you want to fix the same issue For SQL :
Find wich processes are causing issues.
This query will list them:
SELECT TOP 20
qs.sql_handle,
qs.execution_count,
qs.total_worker_time AS Total_CPU,
total_CPU_inSeconds = --Converted from microseconds
qs.total_worker_time/1000000,
average_CPU_inSeconds = --Converted from microseconds
(qs.total_worker_time/1000000) / qs.execution_count,
qs.total_elapsed_time,
total_elapsed_time_inSeconds = --Converted from microseconds
qs.total_elapsed_time/1000000,
st.text,
qp.query_plan
FROM
sys.dm_exec_query_stats AS qs
CROSS APPLY
sys.dm_exec_sql_text(qs.sql_handle) AS st
CROSS APPLY
sys.dm_exec_query_plan (qs.plan_handle) AS qp
ORDER BY
qs.total_worker_time DESC
Fix the processes or related queries you previously detected.
If you need to kill the detected processes, you can find their ids with the previous full processlist and execute the command:
KILL <SPID>
GO
EXEC sp_who2
GO
You can find more alternatives and details at the following source questions/answers/comments:
https://serverfault.com/questions/316922/how-to-detect-the-process-and-mysql-query-that-makes-high-load-on-server How do I find out what is hammering my SQL Server?
You also can use step by step SQL related article: https://www.wearediagram.com/blog/terminating-sql-server-blocking-processes
I have an expensive reporting query that can take 1-20+ seconds to run. (Depending on how much data it has)
Is there a way to kill a mysql process/query from running after a certain amount of time?
I see this:
mysql auto kill query
Is this the best route? I have also read that I should try to improve my queries. I will look into this too, but I am just asking for suggestions on the best route.
First run
show processlist;
then find the query that you want to kill then run
kill "1";
1 is the id of the query you want to kill you have to choose it according to the list
How can i find out if there is transaction open in mySQL? I need to start new one if there is no transaction open, but i don't want to start new one if there is one running, because that would commit that running transaction.
UPDATE:
i need to query database in one method of my application, but that query could be called as part of bigger transaction, or just as it should be a transaction on its own. Changing application to track if it has open a transaction would be more difficult, as it could started from many pieces of code. Although it would be possible, i'm looking for solution that would be faster to implement. Simple if statement in sql would be effortless.
Thank you
I am assuming you are doing this as a one-off and not trying to establish something that can be done programatically. You can get the list of currently active processes using: SHOW PROCESSLIST
http://dev.mysql.com/doc/refman/5.1/en/show-processlist.html
If you want something programatic, then I would suggest an explicit lock on a table, at the beginning of your transaction and release it at the end.
From a script I sent a query like this thousands of times to my local database:
update some_table set some_column = some_value
I forgot to add the where part, so the same column was set to the same a value for all the rows in the table and this was done thousands of times and the column was indexed, so the corresponding index was probably updated too lots of times.
I noticed something was wrong, because it took too long, so I killed the script. I even rebooted my computer since then, but something stuck in the table, because simple queries take a very long time to run and when I try dropping the relevant index it fails with this message:
Lock wait timeout exceeded; try restarting transaction
It's an innodb table, so stuck the transaction is probably implicit. How can I fix this table and remove the stuck transaction from it?
I had a similar problem and solved it by checking the threads that are running.
To see the running threads use the following command in mysql command line interface:
SHOW PROCESSLIST;
It can also be sent from phpMyAdmin if you don't have access to mysql command line interface.
This will display a list of threads with corresponding ids and execution time, so you can KILL the threads that are taking too much time to execute.
In phpMyAdmin you will have a button for stopping threads by using KILL, if you are using command line interface just use the KILL command followed by the thread id, like in the following example:
KILL 115;
This will terminate the connection for the corresponding thread.
You can check the currently running transactions with
SELECT * FROM `information_schema`.`innodb_trx` ORDER BY `trx_started`
Your transaction should be one of the first, because it's the oldest in the list. Now just take the value from trx_mysql_thread_id and send it the KILL command:
KILL 1234;
If you're unsure which transaction is yours, repeat the first query very often and see which transactions persist.
Check InnoDB status for locks
SHOW ENGINE InnoDB STATUS;
Check MySQL open tables
SHOW OPEN TABLES WHERE In_use > 0;
Check pending InnoDB transactions
SELECT * FROM `information_schema`.`innodb_trx` ORDER BY `trx_started`;
Check lock dependency - what blocks what
SELECT * FROM `information_schema`.`innodb_locks`;
After investigating the results above, you should be able to see what is locking what.
The root cause of the issue might be in your code too - please check the related functions especially for annotations if you use JPA like Hibernate.
For example, as described here, the misuse of the following annotation might cause locks in the database:
#Transactional(propagation = Propagation.REQUIRES_NEW)
This started happening to me when my database size grew and I was doing a lot of transactions on it.
Truth is there is probably some way to optimize either your queries or your DB but try these 2 queries for a work around fix.
Run this:
SET GLOBAL innodb_lock_wait_timeout = 5000;
And then this:
SET innodb_lock_wait_timeout = 5000;
When you establish a connection for a transaction, you acquire a lock before performing the transaction. If not able to acquire the lock, then you try for sometime. If lock is still not obtainable, then lock wait time exceeded error is thrown. Why you will not able to acquire a lock is that you are not closing the connection. So, when you are trying to get a lock second time, you will not be able to acquire the lock as your previous connection is still unclosed and holding the lock.
Solution: close the connection or setAutoCommit(true) (according to your design) to release the lock.
Restart MySQL, it works fine.
BUT beware that if such a query is stuck, there is a problem somewhere :
in your query (misplaced char, cartesian product, ...)
very numerous records to edit
complex joins or tests (MD5, substrings, LIKE %...%, etc.)
data structure problem
foreign key model (chain/loop locking)
misindexed data
As #syedrakib said, it works but this is no long-living solution for production.
Beware : doing the restart can affect your data with inconsistent state.
Also, you can check how MySQL handles your query with the EXPLAIN keyword and see if something is possible there to speed up the query (indexes, complex tests,...).
Goto processes in mysql.
So can see there is task still working.
Kill the particular process or wait until process complete.
I ran into the same problem with an "update"-statement. My solution was simply to run through the operations available in phpMyAdmin for the table. I optimized, flushed and defragmented the table (not in that order). No need to drop the table and restore it from backup for me. :)
I had the same issue. I think it was a deadlock issue with SQL. You can just force close the SQL process from Task Manager. If that didn't fix it, just restart your computer. You don't need to drop the table and reload the data.
I had this problem when trying to delete a certain group of records (using MS Access 2007 with an ODBC connection to MySQL on a web server). Typically I would delete certain records from MySQL then replace with updated records (cascade delete several related records, this streamlines deleting all related records for a single record deletion).
I tried to run through the operations available in phpMyAdmin for the table (optimize,flush, etc), but I was getting a need permission to RELOAD error when I tried to flush. Since my database is on a web server, I couldn't restart the database. Restoring from a backup was not an option.
I tried running delete query for this group of records on the cPanel mySQL access on the web. Got same error message.
My solution: I used Sun's (Oracle's) free MySQL Query Browser (that I previously installed on my computer) and ran the delete query there. It worked right away, Problem solved. I was then able to once again perform the function using the Access script using the ODBC Access to MySQL connection.
Issue in my case: Some updates were made to some rows within a transaction and before the transaction was committed, in another place, the same rows were being updated outside this transaction. Ensuring that all the updates to the rows are made within the same transaction resolved my issue.
issue resolved in my case by changing delete to truncate
issue-
query:
delete from Survey1.sr_survey_generic_details
mycursor.execute(query)
fix-
query:
truncate table Survey1.sr_survey_generic_details
mycursor.execute(query)
This happened to me when I was accessing the database from multiple platforms, for example from dbeaver and control panels. At some point dbeaver got stuck and therefore the other panels couldn't process additional information. The solution is to reboot all access points to the database. close them all and restart.
Fixed it.
Make sure you doesn't have mismatched data type insert in query.
I had an issue where i was trying "user browser agent data" in VARCHAR(255) and having issue with this lock however when I changed it to TEXT(255) it fixed it.
So most likely it is a mismatch of data type.
I solved the problem by dropping the table and restoring it from backup.