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Informix - Problem description

Problem IT32060 Status: Closed

CDRLSQN_WAIT IS EXPENSIVE WHEN MANY SESSIONS RUNNING TRANSACTIONS ON
PRIMARY OF HDR PAIR WITH HDR_TXN_SCOPE NEAR_SYNC

product:
INFORMIX SERVER / 5725A3900 / C10 - IDS 12.10
Problem description:
A customer running 12.10.FC7 on linux x86_64 reported a
benchmark was reporting many less transactions per second when
running ~6000 clients against a 52 CPU VP server as compared to
splitting the clients over two 26 CPU VP servers.  The servers
were each primary servers of HDR pairs and DRINTERVAL was set to
0 and HDR_TXN_SCOPE set to NEAR_SYNC.

The 52 CPU VP server was showing hundreds of threads sleeping
forever with stacks like:

0x00000000013e79ef (oninit) yield_processor_mvp
0x00000000013eb1d7 (oninit) mt_yield
0x000000000106550d (oninit) cdrLSNQ_Wait
0x00000000011f55af (oninit) proxyWaitForAllNodesFromPrimary
0x0000000000d3401f (oninit) rscommit
0x000000000078788e (oninit) sqiscommit
0x000000000074c0fa (oninit) sqcommit
0x00000000006bec06 (oninit) aud_sqcommit
0x0000000000a03f44 (oninit) sql_commit
0x0000000000a040c9 (oninit) sq_commit
0x0000000000ad3653 (oninit) sqmain
0x00000000014f7756 (oninit) spawn_thread
0x00000000013c1790 (oninit) th_init_initgls
0x0000000001428327 (oninit) startup

This is a common stack for a thread running in a NEAR_SYNC HDR
environment when the thread is waiting for ack from the
secondary that the commit log record made it to an HDR buffer.

While it is expected to see stacks like these for sqlexec
threads in this HDR environment, if you see a multitude of these
stacks it might indicate another unexpected issue.  In stress
testing designed to mimic comparable work, I observed via
profiling that the cdrLSNQ_Wait function was often a top 10 or
at least a top 20 expensive function.  There is a list in this
function thatgets pretty long and we traverse this list looking
for a particular waiter often having to go several hundred
iterations into the list.  The more threads that are running
transactions and entering this function leads to longer lists
and more and more expensive list traversals which explains why
the customer saw better throughput when they divided clients
across 2 instances.

So, the above stack which shows a sleeping thread can also
indicate a performance issue when hundreds of threads are in
this state.
Problem Summary:
****************************************************************
* USERS AFFECTED:                                              *
* Users of Informix Server prior to 12.10.xC15 and 14.10.xC4.  *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* See Error Description                                        *
****************************************************************
* RECOMMENDATION:                                              *
* Upgrade to Informix Server 12.10.xC15 (when available) or    *
* 14.10.xC4.                                                   *
****************************************************************
Local Fix:
set HDR_TXN_SCOPE to ASYNC
Solution
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
03.03.2020
10.12.2020
10.12.2020
Problem solved at the following versions (IBM BugInfos)
Problem solved according to the fixlist(s) of the following version(s)
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