ASPECT #1

The first thing that caught my eye was this line

InnoDB: Error: trying to load index PRIMARY for table /

This indicates you have a table using the InnoDB Storage Engine

What is interesting about InnoDB is the way a PRIMARY KEY is stored. It is stored in a structure called the gen_clust_index, or more commonly known as the Clustered Index.

My immediate guess is that a certain PRIMARY KEY entry is too big

Please consider some articles on the good, the bad, and the ugly of using long PRIMARY KEYs:

• Long PRIMARY KEY for Innodb tables
• Optimizing Storage Layout for InnoDB tables
• Mysql int vs varchar as primary key (InnoDB Storage Engine?

then see if the <DB Hidden>.<Table Hidden> needs to be redesigned.

ASPECT #2

In terms of your conjecture concerning a parallel truncate table, that sounds kind of dangerous. Why? InnoDB performs TRUNCATE TABLE as DDL not DML. I have written about this before:

• Jul 09, 2012 : What can cause TRUNCATE TABLE to take a really long time?
• Jan 17, 2012 : Problem with InnoDB "per table" file sizes
• Sep 28, 2011 : How to Recover an InnoDB table whose files were moved around

ASPECT #3

Some tuning suggestions

Please add the following to my.ini

[mysqld]
max_allowed_packet=1G
innodb_fast_shutdown=0

Start mysql

In another session, run tail -f <errorlogfile> and watch InnoDB Crash Recovery.

If mysql is fully started back up and InnoDB crash recovery has completed, try to shut mysql down immediately. You may need to resize your InnoDB Transaction Logs.

Sorry for these wild suggestions, but I am flying blind here.

Please post the following in the question:

• your entire my.cnf
• how much RAM is on board

UPDATE 2012-12-05 12:09 EDT

Please do the following:

STEP 01) Add these changes to my.cnf

[mysqld]
max_allowed_packet=1G
innodb_fast_shutdown=0
innodb_thread_concurrency=0

STEP 02) service mysql restart

to make sure mysql comes up

STEP 03) You need to resize ib_logfile0 and ib_logfile1 (24M might be too small)

service mysql stop
cd /var/lib/mysql
mv ib_logfile0 ib_logfile0.bak
mv ib_logfile1 ib_logfile1.bak

STEP 04) Add these changes to my.cnf

[mysqld]
innodb_log_file_size=512M
innodb_log_buffer_size=8M

STEP 05) service mysql start

mysqld will recreate ib_logfile0 and ib_logfile1 512M each

Now, try and see what happens....

UPDATE 2012-12-05 12:18 EDT

In the meantime, please read my ServerFault post on the mysql packet and its sizing implication with regard to the innodb_log_file_size and innodb_log_buffer_size as I learned from someone else's ServerFault post.

UPDATE 2012-12-05 14:28 EDT

I edited all references to customer tables out of this question.

The root cause was a damaged page in ibdata1 with data and index pages mixed inside. I helped Andrew migrate data out, recreate ibdata1 with innodb_file_per_table, and Andrew reloaded the data.

...even surpassing it's theorically maximum possible allocation.

[OK] Maximum possible memory usage: 7.3G (46% of installed RAM)

There is not actually a way to calculate maximum possible memory usage for MySQL, because there is no cap on the memory it can request from the system.

The calculation done by mysqltuner.pl is only an estimate, based on a formula that doesn't take into account all possible variables, because if all possible variables were taken into account, the answer would always be "infinite." It's unfortunate that it's labeled this way.

Here is my theory on what's contributing to your excessive memory usage:

thread_cache_size       = 128

Given that your max_connections is set to 200, the value of 128 for thread_cache_size seems far too high. Here's what makes me think this might be contributing to your problem:

When a thread is no longer needed, the memory allocated to it is released and returned to the system unless the thread goes back into the thread cache. In that case, the memory remains allocated.

^{http://dev.mysql.com/doc/refman/5.6/en/memory-use.html}

If your workload causes even an occasional client thread to require a large amount of memory, those threads may be holding onto that memory, then going back to the pool and sitting around, continuing to hold on to memory they don't technically "need" any more, on the premise that holding on to the memory is less costly than releasing it if you're likely to need it again.

I think it's worth a try to do the following, after first making a note of how much memory MySQL is using at the moment.

Note how many threads are currently cached:

mysql> show status like 'Threads_cached';
+----------------+-------+
| Variable_name  | Value |
+----------------+-------+
| Threads_cached | 9     |
+----------------+-------+
1 row in set (0.00 sec)

Next, disable the thread cache.

mysql> SET GLOBAL thread_cache_size = 0;

This disables the thread cache, but the cached threads will stay in the pool until they're used one more time. Disconnect from the server, then reconnect and repeat.

mysql> show status like 'Threads_cached';

Continue disconnecting, reconnecting, and checking until the counter reaches 0.

Then, see how much memory MySQL is holding.

You may see a decrease, possibly significant, and then again you may not. I tested this on one of my systems, which had 9 threads in the cache. Once those threads had all been cleared out of the cache, the total memory held by MySQL did decrease... not by much, but it does illustrate that threads in the cache do release at least some memory when they are destroyed.

If you see a significant decrease, you may have found your problem. If you don't, then there's one more thing that needs to happen, and how quickly it can happen depends on your environment.

If the theory holds that the other threads -- the ones currently servicing active client connections -- have significant memory allocated to them, either because of recent work in their current client session or because of work requiring a lot of memory that was done by another connection prior to them languishing in the pool, then you won't see all of the potential reduction in memory consumption until those threads are allowed to die and be destroyed. Presumably your application doesn't hold them forever, but how long it will take to know for sure whether there's a difference will depend on whether you have the option of cycling your application (dropping and reconnecting the client threads) or if you'll have to just wait for them to be dropped and reconnected over time on their own.

But... it seems like a worthwhile test. You should not see a substantial performance penalty by setting thread_cache_size to 0. Fortunately, thread_cache_size is a dynamic variable, so you can freely change it with the server running.