SAP Note 18050 - oncheck -pe: Error extents overlap

Symptom:

The extent report, which is generated with the Informix database utility "oncheck -pe" contains an 'Extent overlap' error in connection
with TABLESPACE TABLESPACE Extents. Example:

DBSpace Usage Report: psappool Owner: informix Created: 09/16/94

Chunk: 6 /informix/B20/sapdata/sapdata3 Size Used Free
400000 354071 45929


Disk usage for Chunk 6 Start Length

OTHER RESERVED Pages 0 2
CHUNK FREE LIST PAGE 2 1
TBLSPACE TBLSPACE 3 50
b20:sapr3.t005t 53 8
b20:sapr3.t000 61 8
b20:sapr3.usr03 69 8
b20:sapr3.m_twm9 77 8
b20:sapr3.tbrg 85 8
b20:sapr3.tcurr 93 8
b20:sapr3.usr03 101 128
b20:sapr3.t006d 229 16
b20:sapr3.usr07 245 8
b20:sapr3.tumht 253 16
b20:sapr3.tumwh 269 8
b20:sapr3.usr07 277 8
b20:sapr3.m_mver 285 24
b20:sapr3.m_umcm 309 8
b20:sapr3.m_gwmo 317 8
b20:sapr3.tbrgt 325 8
b20:sapr3.m_twm4 333 8
b20:sapr3.t005 341 8
b20:sapr3.t005s 349 16
b20:sapr3.t005t 365 8
b20:sapr3.t005u 373 24
b20:sapr3.t516t 397 8
b20:sapr3.tcurr 405 32
TBLSPACE TBLSPACE 437 100
b20:sapr3.tcurr 487 8
ERROR: Extents overlap
b20:sapr3.b013 495 8
b20:sapr3.bbpool 503 8
........

1. The report generated by "oncheck -pe" or "oncheck -ce" causes the error "Extents overlap" vor every extent.

2. All ofther "Extents overlap" error messages from "oncheck" indicate a real overlap of extents. In the databank, a "real" extent overlap is a serious matter and absolutely must be corrected by working together with INFORMIX support specialists.

Cause and prerequisites

Re: 1) Due to an Informix bug (PTS #25312: TBCHECK -PE CAN REPORT "EXTENTS OVERLAP" WHEN DISPLAYING TABLESPACE TABLESPACE EXTENTS, BECAUSE IT DOESN'T TAKE INTO ACCOUNT EXTENT DOUBLING), the ONCHECK utility incorrectly issues an extent overlap error for TABLESPACE TABLESPACE extents although the extents do not overlap. Extents vorliegt. This error is caused by the fact that the ONCHECK Utility internally calculates the so called "next extent size" incorrectly at 100 for every additional extent of a TABLESPACE TABLESPACE, although these extents only have 50 pages.
Re: 2) Due to an Informix bug (PTS #37782: ONCHECK -PE REPORTS 'OVERLAPPING EXTENTS' WHEN THEY DON'T REALLY OVERLAP - THIS SEEMS TO BE IBM SPECIFIC) the ONDHCEK untility incorrecly displays an "Extents Overlap" error for every extent, even though no overlap exists. The error appears only with IBM/AIX and HP/HP-UX.

Solution
Please ignore the error message 'ERROR: Extents overlap' in the report generated by "oncheck -pe" in cases 1 and 2, above. There is no extent overlap (you can also check this via the SYSMASTER DB table "sysextents").

Both INFORMIX bugs have been fixed in version 7.10.UD1, that is in SAP Release 3.0 .

Additional key words

PTS PTS_BUG PTS_BUG_25312
PTS PTS_BUG PTS_BUG_37782