i have look around regarding this issues. Recently i faced issues so called unable to conenct any specific mysql server in vb.net. Means in middle of execution of MYSQL, some of execution might interrupted and missing out. So let say i execute 3 mysql operation update, insert and delete, so in middle of execution of this 3 operation, suddenly it pop out "unable to connect any specific mysql HOSTS" and execution for update or insert might missed out. Sometime some columns of execution is missing out and make the execuation incomplete..I tried to change the connection timeout to longger time for 90sec, but still doesnt help. Any suggestion?
You mean instead of doing this
sqlQuery="Update"
executeQuery(sqlQuery, Connection2)
sqlQuery="Update"
executeQuery(sqlQuery, Connection2)
sqlQuery="Insert"
executeQuery(sqlQuery, Connection2)
better doing this
sqlQuery="Update"
sqlQuery="Update"
sqlQuery="Insert"
executeQuery(sqlQuery, Connection2)
I am new to c# and sql server. I'am using SQL Server 2008 and I have 126 tables in my database.
There are 7 transaction tables on which insert/update query fires frequently as there are 30-40 users for my application.
I have written BEGIN TRAN before every query and COMMIT at the end of the query.
Now many-a-times I get error 'Timeout expired ...' when any random user tries to open a form or save some data.
I have written ROLLBACK in my triggers if the trigger throws an error.
But I could not identify on which table BEGIN TRAN has happened or which table is deadlocked.
I have made sure that my connection is proper and is open, then I'am getting this error too
and I couldn't identify from where it is comming.
Does anyone have any idea from where this 'Timeout expired' error is comming and can suggest me some way out?
Does any one have any idea from where this 'Timeout expired' error is coming and can suggest me some way out.
One of the possible reasons is that the transaction cannot acquire lock on some resource(table, row, ...).
In that case you may try to increase the LOCK_TIMEOUT or change the isolation level(if acceptable).
I would suggest reading this article.
I'm using JDBC with mysql. I have a pretty complex series of inserts and updates that I'm doing in a single transaction. This seems to work for the most part, but about 1% of the time I find that the data in one of my tables is in an inconsistent state.
I'm rolling back the transaction if an error occurs, but am not sure how to start debugging. My setup generally looks like:
try {
conn.setAutoCommit(false);
PreparedStatement stmt1 = conn.prepareStatement("insert into table1");
stmt1.executeUpdate();
stmt1.close();
PreparedStatement stmt2 = conn.prepareStatement("update table2");
stmt2.executeUpdate();
stmt2.close();
... more statements ...
conn.commit();
}
catch (Exception ex) {
conn.rollback();
}
I'm using a 2010 version of mysql. I might try updating that, but I have a feeling it's more something in my application code that's causing the inconsistency.
Are there any debugging tools I might find helpful at the database level to help? Any other pointers? I'm using JDBC with all default settings, I wonder if there is any stricter transaction level I need to use for this kind of scenario?
Thanks
----- Note -----
All my tables are InnoDb.
Hm.. Interesting. Yes, it should work. We used really huge transactions accross multiple tables many times, never experienced even strange things...
Are you sure it is not you who produce the inconsistency (whatever this means here, you didn't specify this)? By simply inserting/updating wrong things? :-)
Just an idea - we ran into this several times. Deadlock resolving. DB servers used to handle that. The chance a deadlock occurs is higher if you have several parallel threads and the transaction blocks are manipulating more tables. In this case some of your transactions could be aborted (and rolled back) by the DB server itself. And those transactions will result in an error.
The code you wrote above only rollbacks in the exception case (aborted transaction already rolled back, so it doesn't do too much..), but have you tried to print/log the exceptions? If not you should.
Of course transactions are running separated from each other. But this could explain why you experience this strange behaviour in only 1-2% of the cases...
You should check the logs of your mysql server too. It is also possible the server itself fails for any reason. And one more tip: you may try to run "mysqltop" (or "mtop", hope I remember the name of this tool correctly..). This is able to monitor and show you what happens inside the DB server. However it is mostly used to track the performance of our sqls, this also shows failures. Maybe running this could also help you out...
Perhaps you use DDL (create table, alter table, and so on) in your statements?
I am not sure about MySQL but it may not be able to roll back DDL statements.
For example:
PostgreSQL can rollback DDL,
Oracle performs commit before executing DDL.
See here: http://dev.mysql.com/doc/refman/5.0/en/cannot-roll-back.html
I have quite a simple question I think, but I need a definitive answer. I can't think of way to test out my ideas because it depends on a transient error (out of my control)
SQL Azure is prone to transient errors, timeouts, rejected connections etc. Sometimes on opening the connection, other times when executing a query.
I am inserting a row into SQL Azure via a stored procedure (it's basically a messaging system, so each message should be sent/inserted only once).
If a transient error occurs, my system waits a few seconds, then tries again ... repeating until the stored procedure executes without any errors.
I need the stored procedure to either insert the row and confirm to me that it has been inserted OR to fail completely and NOT insert it.
At the minute, I'm finding that when the database is going through a really bad patch, a message can end up being sent several times.
What would a system that deals with financial transactions do?
Since it's jut one insert statement, am I right in thinking wrapping it in a transaction would have no effect?
Can anyone clarify for me or even point me to some documentation I should read to figure it out myself?
Suppose there is more than just one insert in procedure (some selects after insert?)
You can start transaction in application. that way- if you do commit transaction in application and it succeeds, everything is done.
As per the suggestion by gbn, I added an extra key, not an identity, that I could use to identify duplicates and check on this before inserting
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.