Reducing checkpoint intervals...

I run a very busy OLTP system. Currently, checkpoints are taking between 10 and 20 seconds, and are happening every 5 minutes (as the result of the checkpoint interval being hit.). For obvious reasons, I would like to reduce this. Currently, I see a couple of things to try: * Reduce LRU_MAXDIRTY/LRU_MINDIRTY from their current values of 4/2 to something even lower. (My idea.) I'm leaning towards 1/0 at the moment. * My application vendor suggest that I reduce the number of BUFFERS to 50000, thereby having less memory out there, forcing my buffers to become dirty sonner and thereby be cleaned more frequently, etc... His stated reason for this is that my read cache hit rate is too high. Which of these alternatives would you consider more reasonable? Why? Anyone have a third idea? To me, reducing the number of buffers to get faster checkpoints seems vaguely silly. But, I've Been Wrong Before. (TM) Following this message is a copy of my onconfig for anyone interested. Thanks for your help! Patrick onconfig ---------------------------------------------------------------------------- --------------------------------------------------------------------- #************************************************************************** # # INFORMIX SOFTWARE, INC. # # Title: onconfig.ifx1 # Description: INFORMIX-OnLine Configuration Parameters # #************************************************************************** # Root Dbspace Configuration ROOTNAME rootdbs # Root dbspace name ROOTPATH /Medic/db/ifx1/rootdbs # Path for device containing root dbspace ROOTOFFSET 4 # Offset of root dbspace into device (Kbytes) ROOTSIZE 311292 # Size of root dbspace (Kbytes) # Disk Mirroring Configuration Parameters MIRROR 0 # Mirroring flag (Yes = 1, No = 0) MIRRORPATH # Path for device containingmirrored root MIRROROFFSET 0 # Offset into mirrored device (Kbytes) # Physical Log Configuration PHYSDBS physlog # Location (dbspace) of physical log PHYSFILE 100000 # Physical log file size (Kbytes) # Logical Log Configuration LOGFILES 29 # Number of logical log files LOGSIZE 10000 # Logical log size (Kbytes) # Diagnostics MSGPATH /Medic/db/ifx1/informix.log # System message log file path CONSOLE /Medic/db/ifx1/console.log # System console message path ALARMPROGRAM # Alarm program path # System Archive Tape Device TAPEDEV /dev/rmt1.1 # Tape device path TAPEBLK 1024 # Tape block size (Kbytes) TAPESIZE 30000000 # Maximum amount of data to put on tape (Kbytes) # Log Archive Tape Device LTAPEDEV /dev/null # Log tape device path LTAPEBLK 1024 # Log tape block size (Kbytes) LTAPESIZE 5990000 # Max amount of data to put on log tape (Kbytes) # Optical STAGEBLOB ,0 # INFORMIX-OnLine/Optical staging area # System Configuration SERVERNUM 1 # Unique id corresponding to aOnLine instance DBSERVERNAME ifx1 # Name of default database server DBSERVERALIASES ifx1_tcp1 # List of alternate dbservernames NETTYPE ipcshm,2,400,CPU NETTYPE soctcp,1,50,NET DEADLOCK_TIMEOUT 60 # Max time to wait of lock indistributed env. RESIDENT 0 # Forced residency flag (Yes = 1, No = 0) MULTIPROCESSOR 1 # 0 for single-processor, 1 formulti-processor NUMCPUVPS 12 # Number of user (cpu) vps SINGLE_CPU_VP 0 # If non-zero, limit number of cpuvps to one NOAGE 1 # Process aging AFF_SPROC 0 # Affinity start processor AFF_NPROCS 0 # Affinity number of processors # Shared Memory Parameters LOCKS 150000 # Maximum number of locks BUFFERS 150000 # Maximum number of shared buffers NUMAIOVPS 1 # Number of IO vps PHYSBUFF 64 # Physical log buffer size (Kbytes) LOGBUFF 64 # Logical log buffer size (Kbytes) LOGSMAX 45 # Maximum number of logical log files CLEANERS 48 # Number of buffer cleaner processes SHMBASE 0x30000000 # Shared memory base address SHMVIRTSIZE 256000 # initial virtual shared memorysegment size SHMADD 256000 # Size of new shared memory segments (Kbytes) SHMTOTAL 0 # Total shared memory (Kbytes). 0=>unlimited CKPTINTVL 300 # Check point interval (in sec) LRUS 48 # Number of LRU queues LRU_MAX_DIRTY 4 # LRU percent dirty begin cleaning limit LRU_MIN_DIRTY 2 # LRU percent dirty end cleaninglimit LTXHWM 50 # Long transaction high water markpercentage LTXEHWM 60 # Long transaction high water mark (exclusive) TXTIMEOUT 0x12c # Transaction timeout (in sec) STACKSIZE 32 # 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 workerthreads ON_RECVRY_THREADS 1 # Default number of online workerthreads # 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 /Medic/APPS/Informix71/etc/dr.lostfound # DR lost+found file path # Read Ahead Variables RA_PAGES 10 # Number of pages to attempt to readahead RA_THRESHOLD 5 # Number of pages left before nextgroup # DBSPACETEMP: # OnLine equivalent of DBTEMP for SE. This is the list of dbspaces # that the OnLine SQL Engine will use to create temp tables etc. # If specified it must be a colon separated list of dbspaces that exist # when the OnLine system is brought online. If not specified, or if # all dbspaces specified are invalid, various ad hoc queries will create # temporary files in /tmp instead. DBSPACETEMP tempdb1:tempdb2 # Default temp dbspaces # DUMP*: # The following parameters control the type of diagnostics information which # is preserved when an unanticipated error condition (assertion failure) occurs # during OnLine operations. # For DUMPSHMEM, DUMPGCORE and DUMPCORE 1 means Yes, 0 means No. DUMPDIR /Medic/db/ifx1/tmp # Preserve diagnostics in this directory DUMPSHMEM 0 # Dump a copy of shared memory DUMPGCORE 0 # Dump a core image using 'gcore' DUMPCORE