Обсуждение: pgsql: Improve generation algorithm for database system identifier.
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 Even the intended behavior is obsolete since it was based on wanting to produce a usable value even if we didn't have int64 arithmetic --- a limitation we stopped supporting years ago.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> Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/5035701e07e8bd395aa878465a102afd7b74e8c3 Modified Files -------------- src/backend/access/transam/xlog.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
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 behavior is obsolete since it was based on wanting to produce a 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
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