Exact meaning of TCH in X$BH

From: Lothar Flatz <l.flatz@xxxxxxxxxx>
To: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
Date: Fri, 30 Dec 2022 11:58:11 +0100

Hi guys,

the official definition is : "|X$BH.TCH| is a touch count for the buffer. A high value for |X$BH.TCH| indicates a hot block."
(Source: https://docs.oracle.com/en/database/oracle/oracle-database/19/tgdba/instance-tuning-using-performance-views.html#GUID-64F78817-8B4C-4392-B518-CA31CF728B69).

But the biggest value for tch I have ever seen is 255 (unsigned seven bit integer) . Therefore I think it is not exactly a counter but rather reflects a range.
Can somebody give a detailed explanation? Does the number wrap around? When?

Thanks

Lothar

Follow-Ups:
- Re: Exact meaning of TCH in X$BH
  - From: Stefan Koehler

Other related posts:

» Exact meaning of TCH in X$BH - Lothar Flatz
» Re: Exact meaning of TCH in X$BH- Stefan Koehler
» Re: Exact meaning of TCH in X$BH- Lothar Flatz
» Re: Exact meaning of TCH in X$BH- Martin Klier - Performing Databases GmbH