I/O too high and it almost reach 100%

Question

Experts:
I use berkeley DB to store some index information, the key values are string type and usually they are 20 chars.
Now the hit rate shows it is 98% and db_stat shows no more pages are pageout or pagein. While the I/O rate is too high. I only run the serach command.
2GB Total cache size
1 Number of caches
1 Maximum number of caches
2GB Pool individual cache size
0 Maximum memory-mapped file size
0 Maximum open file descriptors
0 Maximum sequential buffer writes
0 Sleep after writing maximum sequential buffers
0 Requested pages mapped into the process' address space
3245477 Requested pages found in the cache (98%)
57652 Requested pages not found in the cache
32 Pages created in the cache
57616 Pages read into the cache
48199 Pages written from the cache to the backing file
0 Clean pages forced from the cache
0 Dirty pages forced from the cache
0 Dirty pages written by trickle-sync thread
57665 Current total page count
56884 Current clean page count
781 Current dirty page count
262147 Number of hash buckets used for page location
3360554 Total number of times hash chains searched for a page
1 The longest hash chain searched for a page
3245235 Total number of hash chain entries checked for page
41241 The number of hash bucket locks that required waiting (0%)
40939 The maximum number of times any hash bucket lock was waited for (1%)
1872 The number of region locks that required waiting (3%)
0 The number of buffers frozen
0 The number of buffers thawed
0 The number of frozen buffers freed
57676 The number of page allocations
0 The number of hash buckets examined during allocations
0 The maximum number of hash buckets examined for an allocation
0 The number of pages examined during allocations
0 The max number of pages examined for an allocation
23 Threads waited on page I/O
Pool File: DG_11_23_1
4096 Page size
0 Requested pages mapped into the process' address space
2954110 Requested pages found in the cache (98%)
57629 Requested pages not found in the cache
0 Pages created in the cache
57611 Pages read into the cache
48072 Pages written from the cache to the backing file
Pool File: DG_20_24_1
8192 Page size
0 Requested pages mapped into the process' address space
291367 Requested pages found in the cache (99%)
23 Requested pages not found in the cache
32 Pages created in the cache
5 Pages read into the cache
127 Pages written from the cache to the backing file
2GB Total cache size
1 Number of caches
1 Maximum number of caches
2GB Pool individual cache size
0 Maximum memory-mapped file size
0 Maximum open file descriptors
0 Maximum sequential buffer writes
0 Sleep after writing maximum sequential buffers
0 Requested pages mapped into the process' address space
14M Requested pages found in the cache (99%)
58927 Requested pages not found in the cache
32 Pages created in the cache
58891 Pages read into the cache
48199 Pages written from the cache to the backing file
0 Clean pages forced from the cache
0 Dirty pages forced from the cache
0 Dirty pages written by trickle-sync thread
58940 Current total page count
54443 Current clean page count
4497 Current dirty page count
262147 Number of hash buckets used for page location
14M Total number of times hash chains searched for a page (14039718)
1 The longest hash chain searched for a page
13M Total number of hash chain entries checked for page (13921739)
251044 The number of hash bucket locks that required waiting (0%)
250230 The maximum number of times any hash bucket lock was waited for (2%)
1872 The number of region locks that required waiting (3%)
0 The number of buffers frozen
0 The number of buffers thawed
0 The number of frozen buffers freed
58951 The number of page allocations
0 The number of hash buckets examined during allocations
0 The maximum number of hash buckets examined for an allocation
0 The number of pages examined during allocations
0 The max number of pages examined for an allocation
23 Threads waited on page I/O
Pool File: DG_11_23_1
4096 Page size
0 Requested pages mapped into the process' address space
13M Requested pages found in the cache (99%)
58904 Requested pages not found in the cache
0 Pages created in the cache
58886 Pages read into the cache
48072 Pages written from the cache to the backing file
Pool File: DG_20_24_1
8192 Page size
0 Requested pages mapped into the process' address space
618586 Requested pages found in the cache (99%)
23 Requested pages not found in the cache
32 Pages created in the cache
5 Pages read into the cache
127 Pages written from the cache to the backing file
I can not understand why the I/O rate is so high, any expert can give some help?
thanks

Answer 1

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Bogdan Coman