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Re: MDEV-5019 - THREADPOOL - Create Information Schema Table for Threadpool
connection_t = THD class?
it's a different structure/class?
i didn't read the source yet, just high level doubt...
It is a different class.
"Active" connections, i.e connections that currently are executing queries ,
can neither be found in threadpool's waiting_threads, nor there is a
different "active" list for them.
Where they are?
In the global "threads" list. IT is the list of THDs, not threads in the OS
sense of it. Please disregard mixing "threads" with THDs, I know MySQL
terminology gets confusing if one-thread-per-connection is not used.
If you see mentioning of "thread" in threadpool_xxx.cc, then you can be sure
it is about OS threads. For example, waiting_threads list are OS threads,
and not associated with any THDs.
ok i understood that we don't have a flag to show "active/not active" this
should be done with a loop in threads to know if it's active or not, but
what should i look? waiting_thread? queue? "processlist" threads?
Since you say "active/not active", you're talking about are connections,
and not threads. The connections(THDs) are in the global "threads" list.
You already know if they are active or not, nothing needs to be done for
In the current processlist, if Command=Sleep, then the connection is not
the thread group only have threads that are not executing, just queue and
waiting_threads, and executing threads are outside thread pool?
I think you mixing something. Again, I remind that correct naming is when
"thread" is OS thread, and not "THD", or "connection".
So back to the basics : Threadpool consist of worker threads. At any given
moment, there are possibly some threads that do work, and there are other
threads that are idle. Of those that are idle, typically one would be
listening for network events . All threads are part of the threadpool. When
a thread did some work, but became idle, because there is no work to do (all
clients are idle), it adds itself to the list of "idle" threads, aka
Other doubt... a waiting query (inside threadpool and not executing, inside
"waiting_threads") is parsed, it have a THD structure or something that have
the THD->lex? or it just have the network packages "saved in memory"? when
it start execution it will be parsed and the THD will be executed?
Waiting threads do absolutely nothing. They wait until they are woken. They
are not associated with THD, until they do some work. waiting_threads are
not THD, those are OS threads that wait on condition variable.
Usually, a listener thread that I was talking above, will find out that
there is some work, take an idle thread out of the waiting_threads list,
hand it some work to do , and wake it..
So you may want to introduce special handling for those (i.e iterate the
global "threads" list looking for active connections, get corresponding
connection_t* struct from thd->event_scheduler.data, and do something with
it, e.g look which thread group it belongs)
Hum, in this case should be more 'inteligent' have the thread_group at
PROCESSLIST table? and a SQL SELECT could do the job at SQL Layer about
"what connection is active"?
It's nice have a table with all thread, but i think it's the job of
PROCESSLIST right? the point here is the THREAD_POOL information, in other
words, now with you explain, we will have information about queue
(connections without queries, maybe in sleep state) and connections waiting
start (i don't know how is the state of this queries in processlist, do you
PROCESSLIST is about connections, or THDs. It is not about OS threads. It
just happened historically, that each THD in the past always had one
thread, so the terminology got confusing.
In this case (add information at processlist), probably, we will have two
kind of PROCESSLIST one for windows and other for unix, i'm right or wrong?
Well, I would prefer not to have more in processlist than there is now. And
I do not like to have different processlist for different OSes.
On Windows, I doubt you can implement any information_schema plugin for the
threadpool. This is because threadpool is native OS threadpool, and OS
structure representing it PTP_POOL structure is opaque, and there is not
much info you can extract from it (well, maybe you can , if you debug with a
kernel debugger, but not otherwise)
Windows will be a other MDEV
let's start with linux, it's easier than windows hehehe :P
This is wrong, when you talk about threadpool. Windows implementation is
half of Unix in terms of lines of code, and one tens in terms of complexity.
Windows can also be half of what it is now (in LOCS), if I we would to need
to run on XP.
Unix implementation is also much more complicated than it had to be, because
it is built as a workaround for not scaling multithreaded Linux epoll
(http://markmail.org/message/piebp4xosrjv6w7k ). There would not be any need
for thread groups and complicated stuff list that, if multithreaded epoll
From: Maria-developers [mailto:maria-developers-bounces+wlad
=montyprogram.com@xxxxxxxxxxxxxxxxxxx] On Behalf Of Roberto Spadim
Sent: Montag, 16. September 2013 21:20
Subject: [Maria-developers] MDEV-5019 - THREADPOOL - Create Information
Schema Table for Threadpool
I openned a new MDEV https://mariadb.atlassian.net/browse/MDEV-5019 the idea
is expose the threadpool group information like oracle thread pool (more
information about oracle thread pool here:
I can help, but i don't know how access the threadpool at
scheduler.h/scheduler.c from a information schema plugin
1) lock important mutex and others mdl
2) acess variables
3) write information schema based on variables
1 and 2 i don't know how to do :(
can anyone help ? :)
thanks guys :)