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Non-blocking checkpoints in Informix Dynamic Server

Tune Informix Dynamic Server to take advantage of non-blocking checkpoints and RTO_SERVER_RESTART in an online transaction processing environment

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Monitoring checkpoint performance

Table 1. Monitoring checkpoints with onstat -ckp

*AUTO_CKPT=On RTO_SERVER_RESTART=60 Estimated recovery time 7 seconds*
							Critical Sections					Dskflu	Physical Log	Avg	Logical Log	Avg
Interval	Clock Time	Trigger	LSN	Total Time	Flush Time	Block Time	# Waits	Ckpt Time	Wait Time	Long Time	# Dirty Buffers	/Sec	Total Pages	/Sec	Total Pages	/Sec
1	18:41:36	Startup	1:f8	0.0	0.0	0.0	0	0.0	0.0	0.0	4	4	3	0	1	0
2	18:41:49	Admin	1:11c12cc	0.3	0.2	0.0	1	0.0	0.0	0.0	2884	2884	1966	163	4549	379
3	18:42:21	Llog	8:188	2.3	2.0	2.0	1	0.0	2.0	2.0	14438	7388	318	10	65442	2181
4	18:42:44	*User	10:19c018	0.0	0.0	0.0	1	0.0	0.0	0.0	39	39	536	21	20412	816
5	18:46:21	RTO	13:188	197	196.9	0.0	19	0.0	0.0	0.0	158381	804	140253	2921	301751	6286

Max Plog pages/wc

Max Llog pages/sec

Max Dskflush Time

Avg Dskflush pages/sec

Avg Dirty pages/sec

Blocked Time

2954

1160

197

780

2187

Some of the following messages might also be displayed along with the before-mentioned performance advisory information. They are intended to provide suggestions that would lead to better performance.

Physical log is too small for bufferpool size. 
System performance may be less than optimal.
Increase physical log size to at least ##Kb.

Physical log is too small for optimal performance.
Increase the physical log size to at least $ldKb.

Logical log space is too small for optimal performance.
Increase the total size of the logical log space to at least ## Kb.

Physical log is too small for bufferpool size. 
System performance may be less than optimal.
Increase physical log size to at least ##Kb

Transaction blocking has taken place. The physical log is too small.
Please increase the size of the physical log to ##Kb

*Ledger for onstat -ckp*
Item	Units	Description
AUTO_CKPTS	On/Off	Displays if automatic checkpoints feature is on or off
RTO_SERVER_RESTART	Seconds	Displays the RTO policy. 0=RTO policy is off.
Estimated recovery time	Seconds	This is the estimated time it would take the IDS server to perform fast recovery.
Interval	Number	Checkpoint interval id
Clock Time	Wall clock time	This is the wall clock time that the checkpoint occurred
Trigger	Text	There are several events that can trigger a checkpoint. The most common are RTO (trying to maintain the Recovery Time Objective policy), Plog (physical log is 75% full) or Llog (running out of logical log resources). If there is a * in front of the event, that indicated the checkpoint was a transaction blocking checkpoint.
LSN	Log position	Log position of checkpoint
Total Time	Seconds	Total checkpoint duration from request time to checkpoint completion
Flush Time	Seconds	Time to flush bufferpools
Block Time	Seconds	Transaction blocking time
# Waits	Number	Number of transactions that blocked waiting for checkpoint
Ckpt Time	Seconds	This is the amount of time it takes for all transactions to recognize a checkpoint has been requested
Wait Time	Seconds	Average time thread waited for checkpoint
Long Time	Seconds	Longest amount of time a transaction waited for checkpoint
# Dirty Buffers	Number	Number of buffers flushed to disk during checkpoint processing
Dskflu/Sec	Number	Number of buffers flushed to disk per sec during checkpoint processing
Plog Total Pages	Number	Total number of pages physically logged during the checkpoint interval
Plog Avg/Sec	Number	Average rate of physical log activity during the checkpoint interval
Llog Total Pages	Number	Total number of pages logically logged during the checkpoint interval
Llog Avg/Sec	Number	Average rate of logical log activity during the checkpoint interval

Table 2. Monitoring checkpoints with sysmaster

*syscheckpoint*
Column Name	Column Type	Description
intvl	int	Checkpoint interval id
type	char(12)	Blocking or Non-blocking
caller	char(10)	There are several events that can trigger a checkpoint. The most common are RTO (trying to maintain the Recovery Time Objective policy), Plog (physical log is 75% full) or Llog (running out of logical log resources). If there is a * in front of the event, that indicated the checkpoint was a transaction blocking checkpoint.
clock_time	int	This is the wall clock time that the checkpoint occurred. See UNIX localtime() function.
crit_time	float	This is the amount of time it takes for all transactions to recognize a checkpoint has been requested
flush_time	float	Time taken to flush all the bufferpools
cp_time	float	Total checkpoint duration from request time to checkpoint completion
n_dirty_buffs	int	Number of buffers flushed to disk during checkpoint processing
plogs_per_sec	int	Average rate of physical log activity during the checkpoint interval
llogs_per_sec	int	Average rate of logical log activity during the checkpoint interval
dskflush_per_sec	int	Number of buffers flushed to disk per sec during checkpoint processing
ckpt_logid	int	Log position of checkpoint
ckpt_logpos	int	Log position of checkpoint
physused	int	Total number of pages physically logged during the checkpoint interval
logused	int	Total number of pages logically logged during the checkpoint interval
n_crit_waits	int	Number of transactions that blocked waiting for checkpoint
tot_crit_wait	float	Time accumulated by all transactions waiting on checkpoint
longest_crit_wait	float	Longest amount of time a transaction waited for checkpoint
block_time	float	Transaction blocking time

*sysckptinfo*
Column Name	Column Type	Description
ckpt_status	int	0x0011=A checkpoint was blocked because of the physical log running out of resources. 0x0020=A checkpoint was blocked because of the logical log running out of resources. 0x0040=A checkpoint was blocked because of long transactions. 0x1000=Physical log is too small. 0x2000=Logical log space is too small. 0x4000=The physical log is too small for RTO
plogs_per_S	int	Average rate of physical logging activity
llogs_per_S	int	Average rate of logical logging activity
dskF_per_S	int	Average rate of pages flushed to disk
longest_dskF	int	Longest duration of time that it took to flush the bufferpool to disk during checkpoint processing
dirty_pgs_S	int	Average rate of pages being modified
sug_plog_size	int	Suggested physical log size
sug_llog_sz	int	Suggested logical log space size
ras_plog_sp	int	Rate at which fast recovery can restore the physical log
ras_llog_sp	int	Rate at which fast recovery can replay the logical log
boottime	int	Time it takes for the IDS server to boot shared memory and open chunks
auto-ckpts	int	1=On,0=Off
auto_lru	int	1=On,0=Off
cur_intvl	int	Current checkpoint interval id
boottime	int	1=On,0=Off

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