MySQL Bugs: #68827: multiple connections using Shared Memory interfering

Bug #68827	multiple connections using Shared Memory interfering
Submitted:	1 Apr 2013 18:47	Modified:	24 Apr 2013 8:37
Reporter:	Louis at oracle	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Windows	Severity:	S2 (Serious)
Version:	5.6.11	OS:	Windows (window7 64bit)
Assigned to:	MySQL Verification Team	CPU Architecture:	Any
Tags:	Connection, shared memory

Description:
Hello,

I have been experimenting to get more performance out of a visual studio application connected to mysql 5.6.10 via mysql dot net adapter.

Among other things I tried to get more preformance by changing the connection from "localhost;Port=3306" to "Protocol=memory;Shared Memory Name=^FastConn^

That helps a bit (10%), however as soon as I started to use multiple connetions, I got fatal mysql errors in .net adapter

 
 

How to repeat:
I did use multiple connections to decouple tasks:
- reading source
- inserting destination
- logging

Especially when I started using

        cn_dest = New MySqlConnection(connMyDB)

        Call MyLog(3, Now(), "Fill_DB_Vast_DB_Voip", 1, "Gestart", "")

when starting application
        MyCmd.Connection = cn_dest       
        MyCmd.Connection.Open()

when executing inserts
            MyCmd.CommandText = sqlInsertRow
            MyCmd.ExecuteNonQuery()

ending application
   My.Connection.close()

Suggested fix:
No Suggestion

However appart from the bug, note that IMHO, the performance improvement from using shared memory could and should be bigger than 10 - 15%

This could also be a server problem. There is a fix for 5.6.11, it would be interesting if you could wait for server version 5.6.11 to be released and try that...

Bug 13934876 - SHARED MEMORY CONNECTIONS CRASH THE SERVER WHEN ENDING

I switched to 5.6.11 and it looks like the problem is still there.

Louis

the bugfix i mentioned is in 5.6.11. That's a good thing.  However, 5.6.11 still gives some problems.

If I run a single threaded application that connect/disconnect, around 4000 times per second, it's okay.   If I fire up another application, immediately they both catch many errors like;

mysql_real_connect failed: Lost connection to MySQL server at 'reading initial communication packet', system error: 0 (2013)

I will upload a C application here, tomorrow.  I don't think it is a fault of Connector/Net (not sure though, server still has some problems imho).

Hum,

Shane, probably you did not notice, but the error you descibe seems also related to another bug report of me

Bug #68983
Fatal error encountered during data read 

Louis

Verifying as a server bug.

C app, runs fine if one instance runs. Errors out if another instance is run in another window!

Attachment: win_shared_memory.cpp (text/plain), 2.51 KiB.

on my win7 pc, this app makes 12500 connections per second in single thread.

on a very rare occasion this also hits one error during connecting..
perhaps a race between the old thread exiting and new connection already being sent by client.

Shane,

for info I am *not yet* using Multi threading in my (test) application. Reason is simple, I can not even get it running in single proces mode. 
(that holds for all my recent bug reports)

However, even if the application is only one process / thread, within mysql it is not. As descriped in the other bug report, I use one connection per "purpose". Each connection is assiged its own thread, and of course the server has a lot of threads as well.

At the moment the read problem occurs (Bug #68983 Fatal error encountered during data read) the application process has just ended communicating via connection "2 (inserts) and 3 (updates)" and is reading data from conenction "1 ( reads on another table). As indicated each connection has its own thread assigned 

Sincerely,

Louis