SQL Server / JDBC Connectivity Issues - java

I am experiencing some strange behaviour in my Java server application whereby database operations that usually take a few milliseconds are sporadically taking much longer (30s - 170s) to complete. This isn't isolated to a specific query as I've seen the delays occurring for both SQL update and select statements. Also, all of my select statements use the NOLOCK option so I've ruled out possible lock contention.
The last time I saw a delay I managed to capture the following stack trace from JConsole; the update in question typically takes 5ms to complete but this stack trace was accessible for at least 10 - 20 seconds. The trace suggests to me that the statement has been executed but there is some delay in retrieving the result although I could be wrong? Obviously as this was an update statement the only result I'd expect would be the row count (i.e. not a large result set of data).
I saw a "transport level error" in SQL Server Management Studio at around the time of the delay.
One suggestion I've had is that these problems are due to SQL Server resources being exhausted. Has anyone seen anything similar? Can anyone shed any light on this problem?
Thanks in advance.
Stack Trace:
Name: MessageRouterImplThread-2
State: RUNNABLE
Total blocked: 0 Total waited: 224
Stack trace:
java.net.SocketInputStream.socketRead0(Native Method)
java.net.SocketInputStream.read(SocketInputStream.java:129)
com.microsoft.util.UtilSocketDataProvider.getArrayOfBytes(Unknown Source)
com.microsoft.util.UtilBufferedDataProvider.cacheNextBlock(Unknown Source)
com.microsoft.util.UtilBufferedDataProvider.getArrayOfBytes(Unknown Source)
com.microsoft.jdbc.sqlserver.SQLServerDepacketizingDataProvider.signalStartOfPacket(Unknown Source)
com.microsoft.util.UtilDepacketizingDataProvider.getByte(Unknown Source)
com.microsoft.util.UtilByteOrderedDataReader.readInt8(Unknown Source)
com.microsoft.jdbc.sqlserver.tds.TDSRequest.getTokenType(Unknown Source)
com.microsoft.jdbc.sqlserver.tds.TDSRequest.processReply(Unknown Source)
com.microsoft.jdbc.sqlserver.SQLServerImplStatement.getNextResultType(Unknown Source)
com.microsoft.jdbc.base.BaseStatement.commonTransitionToState(Unknown Source)
com.microsoft.jdbc.base.BaseStatement.postImplExecute(Unknown Source)
com.microsoft.jdbc.base.BasePreparedStatement.postImplExecute(Unknown Source)
com.microsoft.jdbc.base.BaseStatement.commonExecute(Unknown Source)
com.microsoft.jdbc.base.BaseStatement.executeUpdateInternal(Unknown Source)
com.microsoft.jdbc.base.BasePreparedStatement.executeUpdate(Unknown Source)
- locked com.microsoft.jdbc.sqlserver.SQLServerConnection#c4b83f
org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:101)
org.springframework.jdbc.core.JdbcTemplate$2.doInPreparedStatement(JdbcTemplate.java:798)
org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:591)
org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:792)
org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:850)
org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:858)
org.springframework.jdbc.core.simple.SimpleJdbcTemplate.update(SimpleJdbcTemplate.java:237)

"...whereby database operations that
usually take a few milliseconds are
sporadically taking much longer (30s -
170s) to complete."
What you are describing sounds like an incorrectly cached query plan, due to out of date statistics (and/or indexes that need rebuilding), or incorrect parameter sniffing. The timeout could be occuring because the server is taking longer than the default connection timeout.
I would talk to your DBA and first get statistics updated, and if that doesn't work get the indexes of the tables involved in the query rebuilt.
Run this on your Database (with the usual caveat about not runninhg in Production without talking to your admin/DBA, and run at own risk etc.):
EXEC sp_updatestats
EXEC sp_refreshview
EXEC sp_msForEachTable 'EXEC sp_recompile ''?'''
Alternatively, you mention time of day being a factor. Could it be that a backup or scheduled job is occuring at that time?
Update: You could kick off a profiler trace: MS SQL Server 2008 - How Can I Log and Find the Most Expensive Queries? but don't restrict to your DB. Such a trace, as long as it is started from SSMS as per that post, is relatively low impact (3-5% ish).

The "transport level error" seems to indicate connectivity problems. Is the database on a separate machine?

Related

Connection to Postgres database lost

On a performance server - with rather a big load, i have a weird behavior.
From one moment in time all the connection the database start to say "connection has been closed".
The only hint so far is this IOException :
Caused by: org.postgresql.util.PSQLException: An I/O error occurred while sending to the backend.
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:314)
at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:430)
at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:356)
at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:168)
at org.postgresql.jdbc.PgPreparedStatement.executeQuery(PgPreparedStatement.java:116)
at org.jboss.resource.adapter.jdbc.WrappedPreparedStatement.executeQuery(WrappedPreparedStatement.java:342)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1812)
at org.hibernate.loader.Loader.doQuery(Loader.java:697)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
at org.hibernate.loader.Loader.doList(Loader.java:2232)
... 73 more
Caused by: java.io.IOException: Tried to send an out-of-range integer as a 2-byte value: 33001
at org.postgresql.core.PGStream.sendInteger2(PGStream.java:211)
at org.postgresql.core.v3.QueryExecutorImpl.sendParse(QueryExecutorImpl.java:1409)
at org.postgresql.core.v3.QueryExecutorImpl.sendOneQuery(QueryExecutorImpl.java:1729)
at org.postgresql.core.v3.QueryExecutorImpl.sendQuery(QueryExecutorImpl.java:1294)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:280)
... 83 more
However i can't really link it to some business scenario for the moment.
Any ideas ?
It's a PostgreSQL driver limitation, the maximum number of parameters for a query is 32768.
You have a query that exceeds that limit - and by doing so the driver has an erratic behavior of closing connections. I encountered that on a JBoss server using Hibernate with PostgreSQL and the connection closing led to a pretty messed up state of the connection pool.
This parameter is described here, in the Parse section:
"Int16 - The number of parameter data types specified".
The solution is to split that long query into smaller ones with a known number of parameters.

Database call stuck at java.net.SocketInputStream.socketRead0(Native Method)

Calls made from Java to SQL server using jtds driver is stuck. We have checked there is no locking or any long running queries on SQL server.
Following is the stack trace from java thread dump. Any one has any idea?
"core-CommandInvoker-thread-7133" prio=5 tid=7362 #### RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:152)
at java.net.SocketInputStream.read(SocketInputStream.java:122)
at java.io.DataInputStream.readFully(DataInputStream.java:195)
at java.io.DataInputStream.readFully(DataInputStream.java:169)
at net.sourceforge.jtds.jdbc.SharedSocket.readPacket(SharedSocket.java:850)
at net.sourceforge.jtds.jdbc.SharedSocket.getNetPacket(SharedSocket.java:731)
at net.sourceforge.jtds.jdbc.ResponseStream.getPacket(ResponseStream.java:477)
at net.sourceforge.jtds.jdbc.ResponseStream.read(ResponseStream.java:146)
at net.sourceforge.jtds.jdbc.ResponseStream.read(ResponseStream.java:128)
at net.sourceforge.jtds.jdbc.TdsData.readData(TdsData.java:767)
at net.sourceforge.jtds.jdbc.TdsCore.tdsRowToken(TdsCore.java:3172)
at net.sourceforge.jtds.jdbc.TdsCore.nextToken(TdsCore.java:2430)
at net.sourceforge.jtds.jdbc.TdsCore.getNextRow(TdsCore.java:802)
at net.sourceforge.jtds.jdbc.JtdsResultSet.next(JtdsResultSet.java:608)
at org.apache.commons.dbcp.DelegatingResultSet.next(DelegatingResultSet.java:207)
at org.apache.commons.dbcp.DelegatingResultSet.next(DelegatingResultSet.java:20
7)
I had the same problem today on Java 8 / JDBI / Postgresql / HikariCP.
Mysteriously adding order by to the query solved the problem.
To be more specific, the resultset needs to be in deterministic order. If there're any ties in the order by, it'll stuck on socketRead0.
Here is an old report that leads me to this solution.

Error : java.lang.OutOfMemoryError: unable to create new native thread : gemfire

Please before marking this duplicate read this : I have gone through all the answers provided for this error and nothing helped in my scenario.
I am doing a server migration where the same thing works well in 32 bit and 64 bit runs out of memory.
I have a windows service which internally points to .exe that spawns java process : I have made all the possible memory improvements in the config file of my .exe :Below:
I am not sure what different behavior is causing this out of memory for 64 bit server.(my java version is 1.8.xx)
#Java Additional Parameters
wrapper.java.additional.1=-XX:+UseConcMarkSweepGC
wrapper.java.additional.2=-XX:+UseParNewGC
wrapper.java.additional.3=-XX:ParallelGCThreads=8
wrapper.java.additional.4=-verbose:gc
# wrapper.java.additional.!!! should be sequence !!!=-Xloggc:D:\apps\Logs\gc.log
# wrapper.java.additional.!!! should be sequence !!!=-XX:+PrintGCDetails
# wrapper.java.additional.!!! should be sequence !!!=-XX:+PrintGCTimeStamps
wrapper.java.additional.5=-XX:MaxDirectMemorySize=128m
wrapper.java.additional.6=-XX:+HeapDumpOnOutOfMemoryError
wrapper.java.additional.7=-Dcom.sun.management.jmxremote.port=34001
wrapper.java.additional.8=-Dcom.sun.management.jmxremote.ssl=false
wrapper.java.additional.9=-Dcom.sun.management.jmxremote.authenticate=false
wrapper.java.additional.10=-XX:CMSInitiatingOccupancyFraction=55
wrapper.java.additional.11=-XX:NewSize=474m
wrapper.java.additional.12=-XX:MaxNewSize=474m
#wrapper.java.additional.13=-XX:PermSize=128m
#wrapper.java.additional.14=-XX:MaxPermSize=128m
wrapper.java.additional.15=-Xss128k
wrapper.java.additional.16=-XX:+CMSIncrementalMode
wrapper.java.additional.17=-XX:+UseCompressedOops
# Initial Java Heap Size (in MB)
wrapper.java.initmemory=1638
# Maximum Java Heap Size (in MB)
wrapper.java.maxmemory=1638
Still i am ending up to have :
[severe 2016/10/24 06:27:46.192 java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Unknown Source)
at com.gemstone.gemfire.internal.SocketCreator.asyncClose(SocketCreator.java:688)
Reading done for the concept here :
Error reading
I am not much into Java things but tried all the things from my side , any help on this will be highly appreciated , i spend huge amount of time on this but not able to reach to any conclusion.
***********Update***************
So basically could figure out that this problem was coming due to excessive creation of thread from Gemfire which exceeds the threshold ~800 threads for Gemfire Java Process.
Here Jconsole tool helped to calculate the thread count , i could see around 200-300 threads from different pool getting created with no purpose apart from usual threads and they have discription as :
Name: pool-9-thread-1
State: WAITING on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject#163b285
Total blocked: 0 Total waited: 2
Stack trace:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(Unknown Source)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)
I'll add more details if i can find more on this !
*******Update 2 : ************
I could manage to see all the threads created by gemfire using Jconsole:
And this number keeps on increasing and after certain point of time i am seeing the OOM issue.Is there any way i can stop this unnecessary threads creation and memory conumption !

odd SQLException - Could not retrieve transation read-only status server

I have a Quartz Job that executes a Stored Procedure in my MySQL database once every 5 minutes, and for some reason, 1 out of 3 executions fails and gives this weird exception. I have searched and searched for what this exception means, but I could not find a solution. Here is the full stack trace:
java.sql.SQLException: Could not retrieve transation read-only status server
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1078)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:951)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:941)
at com.mysql.jdbc.ConnectionImpl.isReadOnly(ConnectionImpl.java:3939)
at com.mysql.jdbc.ConnectionImpl.isReadOnly(ConnectionImpl.java:3910)
at com.mysql.jdbc.PreparedStatement.checkReadOnlySafeStatement(PreparedStatement.java:1258)
at com.mysql.jdbc.CallableStatement.checkReadOnlySafeStatement(CallableStatement.java:2656)
at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1278)
at com.mysql.jdbc.CallableStatement.execute(CallableStatement.java:920)
at com.mchange.v2.c3p0.impl.NewProxyCallableStatement.execute(NewProxyCallableStatement.java:3044)
at org.deadmandungeons.website.tasks.RankUpdateTask.execute(RankUpdateTask.java:30)
at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 1,198,219 milliseconds ago. The last packet sent successfully to the server was 950,420 milliseconds ago.
at sun.reflect.GeneratedConstructorAccessor43.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1121)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3673)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3562)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4113)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2570)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2731)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2812)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2761)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1612)
at com.mysql.jdbc.ConnectionImpl.isReadOnly(ConnectionImpl.java:3933)
... 9 more
Caused by: java.net.SocketException: Connection timed out
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:150)
at java.net.SocketInputStream.read(SocketInputStream.java:121)
at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:114)
at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:161)
at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:189)
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3116)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3573)
... 17 more
So I figured it is timing out because it thinks the MySQL server is in read-only status?
This only happens for this quartz job, and not any other time when I communicate with the database. This execution is of course happening in another thread, but I don't think that would have anything to do with it.
Why would it think the server was in read-only mode?
Also, I don't think "transation" is a word, so there's that...
Sorry for posting on old thread,
As stack trace says
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
This implies the link between JDBC and DB is broken.As per your observation you say 1 out of 3 job invocations fails.
You have these jobs scheduled every 5 minutes and as per trace the last successful message sent to server is ~15 minutes before.
Hence I suspect either
You are procedure is not returning (waiting on something)
The JDBC connection has been invalidated by the firewall/ proxy
It will interesting to see the how connections are managed, As per logs I see you are using c3p0.
You can try setting unreturnedConnectionTimeout and debugUnreturnedConnectionStackTraces. This will give you more insight into connection leaks or db calls which are taking long.
Research takes nowhere, as you guys said, but the error shows what seems to be a Database being populated by two applications at the same time.
Do you have admin privileges on this MySQL server? If you do, you should try setting
FLUSH TABLES WITH READ LOCK;
SET GLOBAL READ_ONLY=ON;
as a test to reproduce the error. Just to warn you, this command makes your database unwritable, so you will not be able to add data in it until you revert this configuration, obviously with
SET GLOBAL READ_ONLY=0;
UNLOCK TABLES;
If the result of this test is positive (same error had been reproduced), you should try isolating applications that are storing data on your database, to find out which one is conflicting with Quartz.
I'm sorry for being vague, but I hope it gives you some help...

Java Quartz Ibatis Cron Issues

I have a java webapp using an ibatis row handler to load a very large dataset (1 million rows in an innodb table). The process is run as a nightly cron job by quartz scheduler. However, after it processes for 6 minutes, it dies with the following stack trace:
WARN [DefaultQuartzScheduler_Worker-8] MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(168) | Could not invoke method 'doBatch' on target object [org.myCron#4adb34]
org.springframework.jdbc.UncategorizedSQLException: SqlMapClient operation: encountered SQLException [
--- The error occurred in org/myCron/mySqlMap.xml.
--- The error occurred while applying a result map.
--- Check the mySqlMap.outputMapping.
--- The error happened while setting a property on the result object.
--- Cause: com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.io.EOFException
STACKTRACE:
java.io.EOFException
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1903)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2402)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2860)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:771)
at com.mysql.jdbc.MysqlIO.nextRow(MysqlIO.java:1289)
at com.mysql.jdbc.RowDataDynamic.nextRecord(RowDataDynamic.java:362)
at com.mysql.jdbc.RowDataDynamic.next(RowDataDynamic.java:352)
at com.mysql.jdbc.ResultSet.next(ResultSet.java:6106)
at org.apache.commons.dbcp.DelegatingResultSet.next(DelegatingResultSet.java:168)
at sun.reflect.GeneratedMethodAccessor71.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:592)
at com.ibatis.common.jdbc.logging.ResultSetLogProxy.invoke(ResultSetLogProxy.java:47)
at $Proxy10.next(Unknown Source)
at com.ibatis.sqlmap.engine.execution.SqlExecutor.handleResults(SqlExecutor.java:380)
at com.ibatis.sqlmap.engine.execution.SqlExecutor.handleMultipleResults(SqlExecutor.java:301)
at com.ibatis.sqlmap.engine.execution.SqlExecutor.executeQuery(SqlExecutor.java:190)
at com.ibatis.sqlmap.engine.mapping.statement.GeneralStatement.sqlExecuteQuery(GeneralStatement.java:205)
at com.ibatis.sqlmap.engine.mapping.statement.GeneralStatement.executeQueryWithCallback(GeneralStatement.java:173)
at com.ibatis.sqlmap.engine.mapping.statement.GeneralStatement.executeQueryWithRowHandler(GeneralStatement.java:133)
at com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.queryWithRowHandler(SqlMapExecutorDelegate.java:649)
at com.ibatis.sqlmap.engine.impl.SqlMapSessionImpl.queryWithRowHandler(SqlMapSessionImpl.java:156)
at com.ibatis.sqlmap.engine.impl.SqlMapClientImpl.queryWithRowHandler(SqlMapClientImpl.java:133)
at org.springframework.orm.ibatis.SqlMapClientTemplate$5.doInSqlMapClient(SqlMapClientTemplate.java:267)
at org.springframework.orm.ibatis.SqlMapClientTemplate.execute(SqlMapClientTemplate.java:165)
at org.springframework.orm.ibatis.SqlMapClientTemplate.queryWithRowHandler(SqlMapClientTemplate.java:265)
at org.myCron.doBatch(MyCron.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:592)
at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:248)
at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:165)
at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:66)
at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)
** END NESTED EXCEPTION **
The stack trace is very vague. The only hints that I see are 'the error happened while setting a property on the result object'. There are only two properties on the result object: a String and an Integer. Both of them permit null values, but my select statements indicate that neither of them have any null values. They both have a proper gettter/setter (which makes sense since the process runs for a while successfully before dying). Every time that the cron runs, it dies at a random point (so it isn't stuck on a particular row).
Note - The method 'doBatch' does exist since that is the method that starts the cron process. If it couldn't find doBatch, it couldn't successfully process the first thousand rows.
I've also tried runnning the job outside of quartz and it also fails there as well. We tried increasing our MySQL net_read_timeout, net_write_timeout, and delayed_insert_timeout but none of these settings helped with the problem. I also tried setting my log4j setting to DEBUG and I did not get any helpful info.
Any other ideas about what I could try?
Sounds like MySQL closed the connection for some reason. Check the MySQL log see if anything shows up. Turn on various logging options for MySQL if necessary.
Also, start printing debug data (including timestamp) from your app - just print everything, then see what the last action was - perhaps you have some rarely triggered conditions in your code that has a bug.
I.e. every single time you talk to MySQL log it before AND after.

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