mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-09-01 19:27:22 +02:00
In the IANA timezone code, tzparse() always tries to load the zone file named by TZDEFRULES ("posixrules"). Previously, we'd hacked that logic to skip the load in the "lastditch" code path, which we use only to initialize the default "GMT" zone during GUC initialization. That's critical for a couple of reasons: since we do not support leap seconds, we *must not* allow "GMT" to have leap seconds, and since this case runs before the GUC subsystem is fully alive, we'd really rather not take the risk of pg_open_tzfile throwing any errors. However, that still left the code reading TZDEFRULES on every other call, something we'd noticed to the extent of having added code to cache the result so it was only done once per process not a lot of times. Andres Freund complained about the static data space used up for the cache; but as long as the logic was like this, there was no point in trying to get rid of that space. We can improve matters by looking a bit more closely at what the IANA code actually needs the TZDEFRULES data for. One thing it does is that if "posixrules" is a leap-second-aware zone, the leap-second behavior will be absorbed into every POSIX-style zone specification. However, that's a behavior we'd really prefer to do without, since for our purposes the end effect is to render every POSIX-style zone name unsupported. Otherwise, the TZDEFRULES data is used only if the POSIX zone name specifies DST but doesn't include a transition date rule (e.g., "EST5EDT" rather than "EST5EDT,M3.2.0,M11.1.0"). That is a minority case for our purposes --- in particular, it never happens when tzload() invokes tzparse() to interpret a transition date rule string found in a tzdata zone file. Hence, if we legislate that we're going to ignore leap-second data from "posixrules", we can postpone the TZDEFRULES load into the path where we actually need to substitute for a missing date rule string. That means it will never happen at all in common scenarios, making it reasonable to dynamically allocate the cache space when it does happen. Even when the data is already loaded, this saves some cycles in the common code path since we avoid a memcpy of 23KB or so. And, IMO at least, this is a less ugly hack on the IANA logic than what we had before, since it's not messing with the lastditch-vs-regular code paths. Back-patch to all supported branches, not so much because this is a critical change as that I want to keep all our copies of the IANA timezone code in sync. Discussion: https://postgr.es/m/20181015200754.7y7zfuzsoux2c4ya@alap3.anarazel.de |
||
---|---|---|
config | ||
contrib | ||
doc | ||
src | ||
.dir-locals.el | ||
.gitattributes | ||
.gitignore | ||
aclocal.m4 | ||
configure | ||
configure.in | ||
COPYRIGHT | ||
GNUmakefile.in | ||
HISTORY | ||
Makefile | ||
README | ||
README.git |
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.