• Admin-Scout-small-Banner
           
    CURSOR Admin-Scout
    get the ultimate tool for Informix
    pfeil  
invispix 10x10
invispix 10x10
Latest versionsfixlist
14.10.xC5 FixList
12.10.xC14.X5 FixList
11.70.xC9.XB FixList
11.50.xC9.X2 FixList
11.10.xC3.W5 FixList
Have problems? - contact us.
Register for free anmeldung-x26
Contact form kontakt-x26
Question in the chat LiveZilla Live Help

Informix - Problem description

Problem IT29960 Status: Closed

INDEX BUILD CAN HAVE BUFFERS X LOCKED FOR A LONG TIME, INCREASING FLUSH
DURATION OF NON-BLOCKING INTERVAL CHECKPOINTS

product:
INFORMIX SERVER / 5725A3900 / C10 - IDS 12.10
Problem description:
When building an index, the code currently looks to see if there
is a pending checkpoint, and if so, it exits critical section
and releases the buffers it holds to allow the checkpoint to
continue.  However, as soon as the it can, it re-enters it's
critical section and then grabs all it's buffers again with X
locks.  If it's able to get it's buffers back before the
checkpoint process was able to flush them, it can then hold the
buffers for a long time causing the checkpoint to not be able to
finish flushing the required buffers to close out the
checkpoint.  This shows up as long duration checkpoints where
all the time is in the flush portion of the checkpoint, and then
would artificially decrease the disk flushes per second in the
onstat -g ckp output (which might cause people to think there
was some IO issue).

You would likely see the following if encountering the problem.

First, the main_loop thread will be running very frequently, but
if you can get a stack trace from it when it is yielding, it
would look like this:

yield_processor
ckpt_dskflush
checkpoint
main_loop
th_init_initgls
startup

Also, you would see some amount of buffers in onstat -b output
that had there xflags set to "80" (to be xlocked) and if you
were to trace the owner of those buffers, they would track back
to xchg threads of part of an index build.

onstat -b output:

IBM Informix Dynamic Server Version 12.10.FC12 -- On-Line (CKPT
INP) -- Up 7 days 23:13:04 -- 251036672 Kbytes

Buffers
address           userthread        flgs pagenum
memaddr           nslots pgflgs xflgs owner             waitlist

Buffer pool page size: 2048
6b19fe858        0                10807 23:1596663
cb17be000        14     10     80    240147388        0
6b1a08ad8        0                10807 23:1607198
cb1840000        12     10     80    16e73c638        0
6b1c65cb8        0                10807 23:1645611
cb3681800        11     10     80    126ec8518        0
6b1fa5b58        0                10807 23:1601752
cb601a000        14     10     80    254441718        0
...

Now we look up owner value in onstat -g ath output:

grep 240147388 onstat.g.ath*
 3319075  2304ff2b0        240147388        1    cond wait
sortproc:0  17cpu         xchg_2.1

Can also look for that owner value in onstat -g ses 0 output,
and we have the following:

session
#RSAM    total      used       dynamic
id       user     tty      pid      hostname
threads  memory     memory     explain
64299    informix -        6008     host1
23       4788224    2794520    off

tid      name     rstcb            flags    curstk   status
...
3319075  xchg_2.1 240147388        Y-B-X--  6815     cond wait
sortproc:0-
...
sqscb info
scb              sqscb            optofc   pdqpriority
optcompind  directives
15e798230        231cd3028        0        10          2
1

Sess       SQL            Current            Iso Lock       SQL
ISAM F.E.
Id         Stmt type      Database           Lvl Mode       ERR
ERR  Vers  Explain
64299      CREATE INDEX   db1                CR  Not Wait   0
0    9.24  Off

Current SQL statement (13) :
  create index "informix".t1_idx1 on "informix".t1 (c1,
     c2, c3) using btree  in s07 online
Problem Summary:
****************************************************************
* USERS AFFECTED:                                              *
* Users of Informix Server prior to 12.10.xC14 and 14.10.xC4.  *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* See Error Description                                        *
****************************************************************
* RECOMMENDATION:                                              *
* Update to Informix Server 12.10.xC14 or 14.10.xC4 (when      *
* available).                                                  *
****************************************************************
Local Fix:
Solution
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
09.08.2019
04.03.2020
04.03.2020
Problem solved at the following versions (IBM BugInfos)
12.10.xC14,
14.10.xC4
Problem solved according to the fixlist(s) of the following version(s)
invispix 10x10
invispix 10x10
invispix 10x10
Technical InfoTechnical Info

Technical Info

DocumentationDocumentation

Documentation

IBM NewsletterIBM Newsletter

IBM Newsletter

Current BugsCurrent Bugs

Current Bugs

Bug ResearchBug Research

Bug Research

Bug FixlistsBug Fixlists

Bug Fixlists

Release NotesRelease Notes

Release Notes

Machine NotesMachine Notes

Machine Notes

Release NewsRelease News

Release News

Product LifecycleProduct Lifecycle

Lifecycle

Media DownloadMedia Download

Media Download

invispix 10x10
Service und SupportService und Support

Service and Support

Informix MonitoringInformix Monitoring

Informix Monitoring

Admin-Scout forInformixAdmin-Scout forInformix

Admin-Scout for Informix

Informix News & InfosInformix News & Infos

Informix News & Infos

This site uses cookies to make it easier for us to provide you with our services. By using our site you agree to the use of cookies.