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Failure to distinguish these cases is the real cause behind the recent reports of Windows builds crashing on 'infinity'::timestamp, which was directly due to failure to establish a value of timezone_abbreviations in postmaster child processes. The postmaster had the desired value, but write_one_nondefault_variable() didn't transmit it to backends. To fix that, invent a new value PGC_S_DYNAMIC_DEFAULT, and be sure to use that or PGC_S_ENV_VAR (as appropriate) for "default" settings that are computed during initialization. (We need both because there's at least one variable that could receive a value from either source.) This commit also fixes ProcessConfigFile's failure to restore the correct default value for certain GUC variables if they are set in postgresql.conf and then removed/commented out of the file. We have to recompute and reinstall the value for any GUC variable that could have received a value from PGC_S_DYNAMIC_DEFAULT or PGC_S_ENV_VAR sources, and there were a number of oversights. (That whole thing is a crock that needs to be redesigned, but not today.) However, I intentionally didn't make it work "exactly right" for the cases of timezone and log_timezone. The exactly right behavior would involve running select_default_timezone, which we'd have to do independently in each postgres process, causing the whole database to become entirely unresponsive for as much as several seconds. That didn't seem like a good idea, especially since the variable's removal from postgresql.conf might be just an accidental edit. Instead the behavior is to adopt the previously active setting as if it were default. Note that this patch creates an ABI break for extensions that use any of the PGC_S_XXX constants; they'll need to be recompiled.
src/timezone/README Timezone ======== This is a PostgreSQL adapted version of the timezone library from: ftp://elsie.nci.nih.gov/pub/tzcode*.tar.gz The code is currently synced with release 2010c. There are many cosmetic (and not so cosmetic) differences from the original tzcode library, but diffs in the upstream version should usually be propagated to our version. The data files under data/ are an exact copy of the latest data set from: ftp://elsie.nci.nih.gov/pub/tzdata*.tar.gz Since time zone rules change frequently in some parts of the world, we should endeavor to update the data files before each PostgreSQL release. At each update, we should check if time zone offsets have changed. Just search for the current or previous year and see what has changed. Sometimes a country changes its time zone offsets, for example Georgia in 2004. Just grepping in the zic database files for 2004 is enough to spot such a change. Then the files under tznames/ should be updated. When there has been a new release of Windows (probably including Service Packs), the list of matching timezones need to be updated. Run the script in src/tools/win32tzlist.pl on a Windows machine running this new release and apply any new timezones that it detects. Never remove any mappings in case they are removed in Windows, since we still need to match properly on the old version.