Hello,

I'm investigating why sequential reads of large Oracle datafiles do
not seem to trigger AIX's read-ahead (vmtune shows maxpgahead = 8),
and looked at the output of fileplace to have a better understanding
of what's going on. From the 3rd range onwards the the ranges seem to
be overlapping. I've never seen this before, what's going on? The
"from" fragment number increments one by one.

AIX version is 5.1.0.0


# fileplace -v ub_indx01_04.ora

File: ub_indx01_04.ora Size: 2097156096 bytes Vol: /dev/gkperflv1
Blk Size: 4096 Frag Size: 4096 Nfrags: 512001 Compress: no
Inode: 527 Mode: -rw-rw---- Owner: oracle8 Group: dba

Logical Fragment
----------------
42195014-42195021 8 frags 32768 Bytes, 0.0%
42195023-42196038 1016 frags 4161536 Bytes, 0.2%
42196041-42196072 32 frags 131072 Bytes, 0.0%
42196042-42196073 32 frags 131072 Bytes, 0.0%
42196043-42196074 32 frags 131072 Bytes, 0.0%
42196044-42196075 32 frags 131072 Bytes, 0.0%
42196045-42196076 32 frags 131072 Bytes, 0.0%
42196046-42196077 32 frags 131072 Bytes, 0.0%
42196047-42196078 32 frags 131072 Bytes, 0.0%
42196048-42196079 32 frags 131072 Bytes, 0.0%
42196049-42196080 32 frags 131072 Bytes, 0.0%
42196050-42196081 32 frags 131072 Bytes, 0.0%
....
42229472-42229503 32 frags 131072 Bytes, 0.0%
42229473-42229504 32 frags 131072 Bytes, 0.0%
42229474-42229505 32 frags 131072 Bytes, 0.0%

512032 frags over space of 34492 frags: space efficiency = 1484.5%
15971 fragments out of 512032 possible: sequentiality = 96.9%


Another file in another filesystem with fragment size of 1024, the
same overlapping occurs, except the "from" here jumps by four:


File: ub_indx06_03.ora Size: 1048580096 bytes Vol: /dev/gkdbtstlv1
Blk Size: 4096 Frag Size: 1024 Nfrags: 1024004 Compress: no
Inode: 1096 Mode: -rw-rw---- Owner: oracle8 Group: dba

Logical Fragment
----------------
75805476-75805507 32 frags 32768 Bytes, 0.0%
75805512-75808759 3248 frags 3325952 Bytes, 0.3%
75821132-75821947 816 frags 835584 Bytes, 0.1%
75821960-75821991 32 frags 32768 Bytes, 0.0%
75821964-75821995 32 frags 32768 Bytes, 0.0%
75821968-75821999 32 frags 32768 Bytes, 0.0%
75821972-75822003 32 frags 32768 Bytes, 0.0%
75821976-75822007 32 frags 32768 Bytes, 0.0%
75821980-75822011 32 frags 32768 Bytes, 0.0%
75821984-75822015 32 frags 32768 Bytes, 0.0%
75821988-75822019 32 frags 32768 Bytes, 0.0%
....

Thanks
Gabor