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Does MaxDataVolumes auto-adjust?

Apr 04, 2017 at 11:16 PM

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In two databases, have noticed MaxDataVolumes changing without an administrator changing it. Is this normal or perhaps an un-documented feature?

In a production database, MaxDataVolumes was originally 12 and now after some months it is 15.

The auto_extend feature is activated and it has been active during this time since the number of data volumes has grown from the original two or three to eleven.

From the kernel messages history:

2016-11-13 13:18:23 RunTime 15: ( ) MaxDataVolumes=12

2016-12-04 13:48:35 RunTime 15: ( ) MaxDataVolumes=12

2017-01-29 09:26:04 0x1 15 RunTime ( ) MaxDataVolumes=15

The second database is for recovery testing and previously had recovered into it an older, smaller backup of the production database.

Recently a current, larger backup was to be recovered into it and the starting point was that there were two data volumes and MaxDataVolumes was 12. The initial recovery attempt failed because the data area was too small. After 9 more data volumes were added to get to 11, a "db_activate recover" was successful and then noticed that MaxDataVolumes was 21.

In neither database is MaxDataVolumes included in the output of "param_extgetall USERDEFINED=YES" and the kernel messages above confirm this in that have the empty parenthesis "( )" rather than "(U)".

"param_getfull MaxDataVolumes" does not say that this is dynamic:

OK

int

1

15

ID MaxDataVolumes

CHANGE OFFLINE

INTERN NO

MANDATORY YES

CLEAR NO

DYNAMIC NO

...

Tested environment:

MaxDB 7.9.08.35 (for SAP Content Server)

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2 Answers

Best Answer
James Zhang
Apr 05, 2017 at 01:20 AM
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Hi Joe,

Just have the same issue with you and our maxdb developer explains how it works:


the mechanism with adding data volumes works as follows.

When you start the database a reserve of 10 volumes is defined which could later be added in online mode.
If they are fully used no more add_volume is possible online.

Then the database has to be stopped to make sure that a new reserve is defined.

When the database is restarted the parameter MaxDataVolumes will automatically be set to a value that allows again 10 volumes to be added.

If you have added for example 6 volumes during online operation the next restart will add a reserve of 6 volumes to make sure that again 10 are available.

Best regards,
James

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Thanks, this explains why when the second database had 11 volumes the parameter went to 21.

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I submitted a documentation feedback item on General Database Parameters to consider whether the entry for this parameter there should have added some of this info.

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Lars Breddemann
Apr 04, 2017 at 11:41 PM
2

If I remember correctly, the parameter gets auto-increased upon restart time.

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Yes, just going to ADMIN mode and back to ONLINE may be enough, since that was the case with the second database where the recovery was done.

Might schedule a restart of the first database or might change the parameter (to 64 probably) and then do a restart since even though it gets auto-increased don't want to rely on that in case there is too much growth before some later restart.

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