pgsql: Improve generation algorithm for database system identifier.

Hi Tom,

On 2014-04-26 19:11:14 +0000, Tom Lane wrote:

Improve generation algorithm for database system identifier.

As noted some time ago, the original coding had a typo ("|" for "^")
that made the result less unique than intended. Even the intended
behavior is obsolete since it was based on wanting to produce a
usable value even if we didn't have int64 arithmetic --- a limitation
we stopped supporting years ago. Instead, let's redefine the system
identifier as tv_sec in the upper 32 bits (same as before), tv_usec
in the next 20 bits, and the low 12 bits of getpid() in the remaining
bits. This is still hardly guaranteed-universally-unique, but it's
noticeably better than before. Per my proposal at
<29019.1374535940@sss.pgh.pa.us>

Modified Files
--------------
src/backend/access/transam/xlog.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

I just noticed that pg_resetxlog.c has a copy of the identifer
generation algorithm that's not been adjusted by that commit.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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Andres Freund <andres@2ndquadrant.com> writes:

I just noticed that pg_resetxlog.c has a copy of the identifer
generation algorithm that's not been adjusted by that commit.

Oh, I'd forgotten about that :-(. Thanks, will fix.

regards, tom lane

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