Re: Performance Problem with many buffer wait
Your bufwait ratio is 17.4% which is bad, the value should be in the range
1-10% with values under 7% giving best results. Tunables which affect the
ratio are: LRUS, BUFFERS, RA_PAGES, RA_THRESHOLD. If you have more than
16 or 20 users then start by increasing LRUS, the current value can not
support more than 16 or 20 active users without LRU contention (avoid
LRUS=64 it triggers a bug). See other posts of mine to find the ratio
formula.
Increasing the number of buffers can also help and, I just learned this
AM, apparently increasing the RA parameters may releave some pressure on
the LRUS be makeing more data available before it is needed thereby
reducing the number of LRU latch requests.
Art S. Kagel
Grace Kan wrote:
>
> Hi all informix expert,
>
> I am now using Informix Online 7.30, and I experience a lot of
> buffer wait, that is a B flag in first position in onstat -u, which make
> my informix database extremely slow.
>
> c4ad7d24 B--PR-- 50686 hwchung ttyud c22403a8 0 1 1238
> 64
>
> So why this happen and how to avoid it. And one more question,
> why not the onstat -u show lock wait ( L flag in the first position)
> rather than buffer wait, as user thread getting a buffer by obtain a
> share lock or exclusive lock on that buffer.
>
> Looking forward to have your reply
>
> Best Regards,
> Grace
> ps. attached is onstat -c and onstat -p
>
> #**************************************************************************
>
> #
> # INFORMIX SOFTWARE, INC.
> #
> # Title: onconfig.01
> # Description: INFORMIX-OnLine Configuration Parameters
> #
> #**************************************************************************
>
> # Root Dbspace Configuration
>
> ROOTNAME rootdbs # Root dbspace name
> ROOTPATH /dev/rootdcs.1 # Path for device containing root> dbspace
> ROOTOFFSET 0 # Offset of root dbspace into device
> (Kbytes)
> ROOTSIZE 204800 # Size of root dbspace (Kbytes)>
> # Disk Mirroring Configuration Parameters
>
> MIRROR 0 # Mirroring flag (Yes = 1, No = 0)
> MIRRORPATH # Path for device containing mirrored> root
> MIRROROFFSET 0 # Offset into mirrored device (Kbytes)>
> # Physical Log Configuration
>
> PHYSDBS rootdbs # Location (dbspace) of physical log
> PHYSFILE 10240 # Physical log file size (Kbytes)>
> # Logical Log Configuration
>
> LOGFILES 94 # Number of logical log files
> LOGSIZE 4000 # Logical log size (Kbytes)>
> # Diagnostics
>
> MSGPATH /usr2/informix7/co2dcs.log # System message log file
> path
> CONSOLE /dev/console # System console message path> ALARMPROGRAM /usr2/informix7/log_full.sh # Alarm program path
>
> # System Archive Tape Device
>
> TAPEDEV /dev/rmt/0m # Tape device path
> TAPEBLK 16 # Tape block size (Kbytes)
> TAPESIZE 8192000 # Maximum amount of data to put on tape
> (Kbytes)>
> # Log Archive Tape Device
>
> LTAPEDEV /dev/rmt/0m # Log tape device path
> LTAPEBLK 16 # Log tape block size (Kbytes)
> LTAPESIZE 8192000 # Max amount of data to put on log tape
> (Kbytes)>
> # Optical
>
> STAGEBLOB # INFORMIX-OnLine/Optical staging area
>
> # System Configuration
>
> SERVERNUM 6 # Unique id corresponding to a OnLine> instance
> DBSERVERNAME co2dcs # Name of default database server
> DBSERVERALIASES # List of alternate dbservernames
> NETTYPE ipcshm,1,512,CPU # Configure poll thread(s) for nettype
> NETTYPE soctcp,1,128,NET # Configure poll thread(s) for nettype
> DEADLOCK_TIMEOUT 60 # Max time to wait of lock in> distributed env.
> RESIDENT 1 # Forced residency flag (Yes = 1, No =
> 0)
>
> MULTIPROCESSOR 1 # 0 for single-processor, 1 for> multi-processor
> NUMCPUVPS 2 # Number of user (cpu) vps
> SINGLE_CPU_VP 0 # If non-zero, limit number of cpu vps> to one
>
> NOAGE 0 # Process aging
> AFF_SPROC 0 # Affinity start processor
> AFF_NPROCS 0 # Affinity number of processors>
> # Shared Memory Parameters
>
> LOCKS 200000 # Maximum number of locks
> BUFFERS 20000 # Maximum number of shared buffers
> NUMAIOVPS 11 # Number of IO vps
> PHYSBUFF 128 # Physical log buffer size (Kbytes)
> LOGBUFF 128 # Logical log buffer size (Kbytes)> LOGSMAX 100 # Maximum number of logical log files
> CLEANERS 8 # Number of buffer cleaner processes
> SHMBASE 0x0 # Shared memory base address
> SHMVIRTSIZE 163840 # initial virtual shared memory segment> size
> SHMADD 30000 # Size of new shared memory segments
> (Kbytes)
> SHMTOTAL 0 # Total shared memory (Kbytes).
> 0=>unlimited
> CKPTINTVL 300 # Check point interval (in sec)
> LRUS 16 # Number of LRU queues
> LRU_MAX_DIRTY 5 # LRU percent dirty begin cleaning limit
>
> LRU_MIN_DIRTY 2 # LRU percent dirty end cleaning limit
> LTXHWM 50 # Long transaction high water mark> percentage
> LTXEHWM 60 # Long transaction high water mark
> (exclusive)
> TXTIMEOUT 0x12c # Transaction timeout (in sec)
> STACKSIZE 128 # Stack size (Kbytes)>
> # System Page Size
> # BUFFSIZE - OnLine no longer supports this configuration parameter.
> # To determine the page size used by OnLine on your platform
> # see the last line of output from the command, 'onstat -b'.
>
> # Recovery Variables
> # OFF_RECVRY_THREADS:
> # Number of parallel worker threads during fast recovery or an offline
> restore.
> # ON_RECVRY_THREADS:
> # Number of parallel worker threads during an online restore.
>
> OFF_RECVRY_THREADS 10 # Default number of offline worker> threads
> ON_RECVRY_THREADS 1 # Default number of online worker> threads
>
> # Data Replication Variables
> # DRAUTO: 0 manual, 1 retain type, 2 reverse type
> DRAUTO 0 # DR automatic switchover
> DRINTERVAL 30 # DR max time between DR buffer flushes
> (in sec)
> DRTIMEOUT 30 # DR network timeout (in sec)
> DRLOSTFOUND /dev/null # DR lost+found file path>
> # Backup/Restore variables
> BAR_ACT_LOG /tmp/bar_act.log
> BAR_MAX_BACKUP 0
> BAR_RETRY 1
> BAR_NB_XPORT_COUNT 10
> BAR_XFER_BUF_SIZE 31>
> # Read Ahead Variables
> RA_PAGES 20 # Number of pages to attempt to