Hi Wlad! thanks for the explain...

for now, just unix is ok, windows is a second step =]

Just some doubts...

2013/9/17 Vladislav Vaintroub <wlad@montyprogram.com>

Hi Roberto,

The structures you need are in sql/threadpool_unix.cc
Global all_groups array contains all thread groups . Every thread_group_t has list of waiting threads , called “waiting_threads”, and queue of not yet handled requests, called “queue” (request is represented by connection_t ), a listener etc.

connection_t = THD class?

it's a different structure/class?

i didn't read the source yet, just high level doubt...

“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?

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?

the thread group only have threads that are not executing, just queue and waiting_threads, and executing threads are outside thread pool?

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?

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 know?)

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?

I'm thinking about some thing like

current processlist:

ID	QUERY_ID	USER	HOST	DB	COMMAND	TIME	STATE	INFO	TIME_MS	STAGE	MAX_STAGE	PROGRESS	MEMORY_USED	EXAMINED_ROWS
1962	436279	rspadim	***:48785	spd_cashflow	Query	0	executing	select * from information_schema.PROCESSLIST	0.321	0	0	0.000	83280	0

add two columns:

SCHEDULER ENUM('no-threads','one-thread-per-connection','pool-of-threads','daemon-plugin') NOT NULL DEFAULT 'one-thread-per-connection',

THREADPOOL_GROUP BIGINT UNSIGNED DEFAULT NULL COMMENT 'NULL = not thread pool connection'

the THREADPOOL_GROUP column is a INT? BIGINT? UNSIGNED? NOT NULL?

maybe this could be allowed without the thread-poll and we could use NULL to show that's a "one-thread-one-connection" or "no-threads" or "daemon-plugin", what you think?

in patch of QUERY_ID column (MDEV-4911) we had *many* test cases changes, but it's not a problem =], just change one time instead of add one column, write a patch, add other column write other patch...

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 (https://mariadb.atlassian.net/browse/MDEV-5046) =)

let's start with linux, it's easier than windows hehehe :P

Wlad

From: Maria-developers [mailto:maria-developers-bounces+wlad=montyprogram.com@lists.launchpad.net] On Behalf Of Roberto Spadim
Sent: Montag, 16. September 2013 21:20
To: maria-developers@lists.launchpad.net
Subject: [Maria-developers] MDEV-5019 - THREADPOOL - Create Information Schema Table for Threadpool

Hi guys!
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: http://mikaelronstrom.blogspot.com.br/2011_10_01_archive.html)

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 :)

--
Roberto Spadim

Roberto Spadim
SPAEmpresarial