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Informix - Problem description

Problem IT29534 Status: Closed

CHECKPOINT MAY HANG FOREVER WITH CONCURRENT PARALLEL INDEX BUILD

product:
INFORMIX SERVER / 5725A3900 / C10 - IDS 12.10
Problem description:
Under some conditions, a blocking checkpoint may get hung and
never complete if some sort of parallel index build is happening
concurrently.  The index build may be just a create index
statement, or a set object enabled.

The checkpoint hang occurs because the main_loop thread is
unable to flush all the dirty buffers required for that
checkpoint interval.  You may see it in a stack that looks like
this:

mt_yield
ckpt_dskflush
checkpoint
main_loop
th_init_initgls
startup

So main_loop keeps trying to flush the required buffers, but
there will be some number of buffers that can be seen in onstat
-b output that will be flagged as dirty and they will be xlocked
and the thread that owns those buffers will be waiting on the
checkpoint condition.

Here is onstat -b output showing 2 dirty buffers (the "flgs"
field will have the presence of 1 in it's value) they are
xlocked (so "xflgs" field will be = "80") and both these buffers
are owned by the same thread.  Following the onstat -b output
will be the stack trace of that thread along with it's onstat -g
ath output showing it waiting on the checkpoint condition.

onstat -b

IBM Informix Dynamic Server Version 12.10.FC12 -- On-Line (CKPT
REQ) -- Up 02:36:25 -- 545336 Kbytes
Blocked:CKPT

Buffers
address           userthread        flgs pagenum
memaddr           nslots pgflgs xflgs owner             waitlist


Buffer pool page size: 2048
5976e758         0                807  8:1415           5a9fa000
21     10     80    4b8a3888         0
59774ab8         0                807  8:1574           5aa49800
20     10     80    4b8a3888         0
 2 modified, 90000 total, 131072 hash buckets, 2048 buffer size

onstat -g ath | grep 4b8a3888
Threads:
 tid     tcb              rstcb            prty status
vp-class       name
 92       4c663648         4b8a3888         1    cond wait  cp
8cpu         xchg_1.0

onstat -g stk 92

yield_processor_mvp
mt_fast_wait
critwait
critenter
btusearch
btadditem
btmakeroot
close_btmrg
producer_thread
startup

The session for that thread was running the following sql

Current SQL statement (4) :
  create index t1_idx on t1(c1,c2,c3,c4,c5) using btree in
dbsidx
Problem Summary:
****************************************************************
* USERS AFFECTED:                                              *
* Users of IDS prior to version 12.10.xC14.                    *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* Checkpoint may hang forever with concurrent parallel index   *
* build.                                                       *
****************************************************************
* RECOMMENDATION:                                              *
****************************************************************
Local Fix:
Solution
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
24.06.2019
20.09.2019
20.09.2019
Problem solved at the following versions (IBM BugInfos)
12.10.xC14
Problem solved according to the fixlist(s) of the following version(s)
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