LRU_MAX_DIRTY, LRU_MIN_DIRTY (Informix)
LRU_MAX_DIRTY, LRU_MIN_DIRTY (Informix)
Definition
These parameters from the Informix
ONCONFIG file are expressed as percentages and have the following meanings:You can use
LRUS with LRU_MAX_DIRTY and LRU_MIN_DIRTY to control how often pages are flushed to disk between full checkpoints. In this way you can shorten the checkpoint by writing as many pages as possible outside the checkpoint.Use
For up-to-date recommendations, see SAP Note 41360.
You can display the current
LRUS usage with the onstat –R command as in the following example:
25 buffer LRU queue pairs | ||||
# |
f/m |
length |
% of pair |
total |
0 |
f |
9454 |
95.3% |
9918 |
1 |
m |
464 |
4.7% |
|
2 |
f |
9463 |
94.5% |
10009 |
3 |
m |
546 |
5.5% |
|
4 |
f |
9384 |
93.7% |
10016 |
5 |
m |
632 |
6.3% |
|
... |
||||
48 |
f |
9429 |
94.0% |
10028 |
49 |
m |
599 |
6.0% |
9998 |
13888 dirty,249978 queued,250000 total,262144 hash buckets,2048 buff | ||||
start clean at 8% (of pair total) dirty, or 800 buffs dirty,stop at 2% | ||||
If the changed
LRUS queues are permanently longer than LRU_MAX_DIRTY , you did not configure enough LRUS or CLEANERS . Increase the number of LRUS first. If nothing changes, increase the number of CLEANERS , too. Check the results each time with onstat -R .Consider the dependence of these parameters on the
BUFFERS parameter when you are tuning. The following example shows the effect of increasing BUFFERS :
On a system with
If you increase
BUFFERS to 40,000 without changing LRU_MIN_DIRTY , there could be 8,000 modified pages at checkpoint time.
See also:
Monitoring Checkpoints (Informix) CLEANERS (Informix) LRUS (Informix)