Folks, I had another issue now regarding to libmysqlclient-dev api
Here the story:
I created about 10 threads which will do SQL query in every 2 seconds, and loop,
in math you could say 10 query in 2 seconds in the same time, and it ended itself with MySQL error message lost connection during SQL query
Questions:
in these case, is my algorithm will always cause MySQL server lost connection ?
if so, will these issue appear if I use another db (say Oracle, Postgre, etc), or result will same?
What are you doing in the thread that loses the connection, and what are the other threads doing at the same time?
It depends. Consider your question the equivalent of "my car makes a funny noise when I drive down Street X. Should I get a new car?". If the noise is due to you falling into a pothole, changing cars won't make any difference.
well everything is now run better once
the MYSQL* is protected by posix-mutex https://computing.llnl.gov/tutorials/pthreads/#MutexLocking
the code compiiled with mysql_config --libs_r parameter
thats for now, any addition ?
Related
I have a MySQL database that I am running very simple queries against as part of a webapp. I have received reports from users starting today that they got an error saying that their account doesn't exist, and when they log in again, it does (this happened to only a few people, and only once to each, so clearly it is rare). Based on my backend code, this error can only occur if the same query returns 0 row the first time, and 1 row the second. My query is basically SELECT * FROM users WHERE username="...". How is this possible? My suspicion is that the hard disk is having I/O failures, but I am unsure because I would not expect MySQL to fail silently in this case. That said, I don't know what else it could be.
This could be a bug with your mysql client (Though I'm unsure as to how the structure of your code is, it could just be bad query). However let's assume that your query has been working fine up until now with no prior issues, so we'll rule out bad code.
With that in mind, I'm assuming it's either a bug in your mysql client or your max connection count is reached (Had this issue with my previous host - Hostinger).
Let's say your issue is a bug in your mysql client, set your sessions to per session basis by running this
SET SESSION optimizer_switch="index_merge_intersection=off";
or in your my.cnf you can set it globally
[mysqld] optimizer_switch=index_merge_intersection=off
As for max connection you can either increase your max_connection value (depending if your host allows it), or you'll have to make a logic to close the mysql connection after a query execution.
$mysqli->close();
I'm using MySQL workbench to run a query. The query is reasonably big. When I limit the results to say 50 records the results are as expected. But when I remove the limit, the query runs for ~ 5 minutes then prompts me to re-enter my password. After doing so I see the query has not run and has stopped working.
It seems like there is a setting that kicks me off after a certain amount of time but I cannot see it in the drop down menus.
Has anyone experienced this? Any advice?
** Update**
Query ran and Workbench says results returned but they are not and I got the screen shot error pop up here:
It sounds like one of three things are the likely culprit.
MySql Workbench may be timing out.
This may help with #1
Go to Edit -> Preferences -> SQL Editor and set to a higher value this
parameter: DBMS connection read time out (in seconds). For instance:
86400.
Close and reopen MySQL Workbench. Kill your previously query that
probably is running and run the query again.
The mySQL server is timing out
You will need access to the server's timeout configuration
Something network related (but far less likely if your timeout happens consistently at around 5 mins)
There are a number of factors that might need adjusting.
If #2, you will need access to the server's timeout configuration
If #3, well, there are a number of factors that might need adjusting.
I have one problem with FEDERATED table in MySQL. I have one server (MySQL version 5.0.51a), who serve to store client data and actually nothing more. The logic database are stored in another server (version 5.1.56), sometimes it should handle that data from first server. So the second server have one FEDERATED table, which connect to the first server.
Actually, it has worked without any problems, but recently I got strange errors with this solution. Some kind of queries on second server cannot be performed correctly.
For example SELECT * FROM table - doesn't work. It hangs exactly 3 minutes and then gives:
Error Code: 1159 Got timeout reading communication packets
Ok, I checked table on the first server and it's Ok. Then I tried some another queries to FEDERATED table and they work...
For example, query like SELECT * FROM table WHERE id=x returns the result. Probably it could have problem with size of result, so I tried query with dummy WHERE-clause like SELECT * FROM table WHERE id > 0 - and it also works...
Finally I found a "solution", which helped only for two days - on the first server I made a copy of table, and on second server I re-declared a new FEDERATED table with new connection string to this copy. And it works, but after two days the same problem with new copied table.
I've already talk with both server providers, they see no problems, everything seems to work and other hosting provider is the causer of problems.
I've checked all variables in MySQL and there is no timeout parameter with 3 minutes etc. So how can I deal so kind of problems? It seems to be something automatic on network or database side, but I don't know, how to detect the reason of problems.
Do You have any ideas?
You may try checking MTU size settings for network interfaces on both servers.
This warning is logged when idle threads are killed by wait_timeout.
Normally, the way to avoid threads getting killed by wait_timeout is to call mysql_close() in scripts when the connection is no longer needed. Unfortunately that doesn't work for queries made through federated tables because the query and the connection are not on the same server.
For example, when a query is executed on server A of a federated table (pointing to data on server B), it creates a connection on server B. Then when you run mysql_close() on server A it obviously can not close the connection that was created on server B.
Eventually the connection gets killed by mysql after the number of seconds specified in "wait_timeout" have passed (the default is 8 hours). This generates the warning in your mysqlerror.log "Got timeout reading communication packets"
I am getting the error stated in my post title. I have two tables. The first one, large is over than 4000,000 records and the second, small one is arounf 7000 records. I want to search for the value in the samll table and if found, I want to extract the whole record from the large table. The command never executed and always lose the connection with the database. I tried to limit the out put to 50 records only, the same thing happens. Please help me. If I need something like indexing (I read this might solve such performance problems, please clarify to me how. I'm not a DBA).
select * from db.large, db.small
where large.value=small.value;
*EDIT: * I use MySQL workbench 5.2.41 CE.
At one point on a previous project, I could actually crash the MySQL server reproducibly with a pretty simple query. In the code that called the database, I saw the same error message. Can you verify that the MySQL server's process ID is the same before and after the query? Chances are that your OS restarts the MySQL server immediately after the crash, and the MySQL command line client automatically reconnects (though it emits a notice when it does).
Having a major hair-pulling issue with extremely slow inserts from Delphi 2010 to a remote MySQL 5.09 server.
So far, I have tried:
ADO using MySQL ODBC Driver
Zeoslib v7 Alpha
MyDAC
I have used batching and direct insert with ADO (using table access), and with Zeos I have used SQL insertion with a Query, then used Table direct mode and also cached updates Table mode using applyupdates and commit. With MyDAC I used table access mode, then direct SQL insert and then batched SQL insert
All technologies I have tried, I set compression on and off with no discernable difference.
So far I have seen a pretty much the same across the board 7.5 records per second!!!
Now, I would from this point assume that the remote server is just slow, but the MySQL Workbench is amazingly fast, and the Migration toolkit managed the initial migration very quickly (to be honest, I don't recall how quickly - which kind of means that it was quick)
Edit 1
It is quicker for me to write the sql to a file, upload the file to the server via ftp and then import it direct on the remote server - I wonder if they perhaps are throttling incoming MySQL traffic, but that doesn't explain why the MySQL Workbench was so quick!
Edit 2
At the most basic level, the code has been:
while not qMSSQL.EOF do
begin
qMySQL.SQL.Clear;
qMySQL.SQL.Add('INSERT INTO tablename (fieldname1) VALUES (:fieldname1)');
qMySQL.ParamByName('fieldname1').asString:=qMSSQL.FieldByName('fieldname1').asString;
qMySQL.ExecSQL;
qMSSQL.Next;
end;
I then tried
qMySQL.CachedUpdates:=true;
i:=0;
while not qMSSQL.EOF do
begin
qMySQL.SQL.Clear;
qMySQL.SQL.Add('INSERT INTO tablename (fieldname1) VALUES (:fieldname1)');
qMySQL.ParamByName('fieldname1').asString:=qMSSQL.FieldByName('fieldname1').asString;
qMySQL.ExecSQL;
inc(i);
if i>100 then
begin
qMySQL.ApplyUpdates;
i:=0;
end;
qMSSQL.Next;
end;
qMySQL.ApplyUpdates;
Now, in this code with CachedUpdates:=False (which obviously never actually wrote back to the database) the speed was blisteringly fast!!
To be perfectly honest, I think it's the connection - I feel it's the connection... Just waiting for them to get back to me!
Thanks for all your help!
You can try AnyDAC and it Array DML feature. It may speedup a standard SQL INSERT for few times.
Sorry that this reply comes long after you asked the question.
I had a similar problem. BDS2006 to MySQL via ODBC across the network - took 25 minutes to run - around 25 inserts per second. I was using a TDatabase connection and attached the TTable Tquery to it. Prepared the SQL statements.
The major improvement was when I started starting transactions within the loop. A simple example, Memebrships have Member Period. Start a transaction before the insert of the Membership and Members, Commit after. The number of memberships was 01585 and before transactions it took 279.90 seconds to process all the Membership records but after it took 6.71 seconds.
Almost too good to believe and am still working through fixing the code for the other slow bits.
Maybe Mark you have solved your problem but it may help someone else.
Are you using query parameters? The fastest way to insert should be using plain queries and parameters (i.e. INSERT INTO table (field) VALUES (:field) ), preparing the query and then assigning parameters and executing as many times as required within a single transaction - committing at the end (don't use any flavour of autocommit)
That in most databases avoids hard parses each time the query is executed, which requires time. Parameters allow the query to be parsed only once, and then re-executed many times as needed.
Use the server facilites to check what's going on - many offer a way to inspect what running statements are doing.
I'm not sure about ZeosLib, but using ADO with ODBC driver, you will not get the fastest way to insert the records, here few step that may make your insertion faster:
Use Mydac for direct access, they work without the slow ODBC > ADO > OLEDB > MySqlLib to connect to Mysql.
Open the connection at first before the insertion.
if you have large insertion such as 1000 or more, try use transaction and commit after 100 record or more depend on number of records.
Point 3 may makes your insertion faster even with ZeosLib or ADO.
You've got two separate things going on here. First, your Delphi program is creating Insert statements and sending them to the DB server, and then the server is handling them. You need to examine both ends to find the bottleneck. I'm not to familiar with MySql tools, but I bet you could find a SQL profiler for it easily enough. Use it to profile your inserts from the Delphi app, and compare it to running inserts from the Workbench tool and see if there's a significant difference.
If not, then the slowdown is in your app. Try hooking it up to Sampling Profiler or some other profiling tool that understands Delphi, and it'l show you where you're spending lots of time on. Once you know that, then you can work on attacking the problem, or maybe come back here to ask a more specific question. But until you know where the problem is coming from, any answers you get here are just gonna be educated guesses at best.