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Commitc521d5a

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Improve performance of timezone loading, especially pg_timezone_names view.
tzparse() would attempt to load the "posixrules" timezone database file oneach call. That might seem like it would only be an issue when selecting aPOSIX-style zone name rather than a zone defined in the timezone database,but it turns out that each zone definition file contains a POSIX-style zonestring and tzload() will call tzparse() to parse that. Thus, when scanningthe whole timezone file tree as we do in the pg_timezone_names view,"posixrules" was read repetitively for each zone definition file. Fixthat by caching the file on first use within any given process. (We cacheother zone definitions for the life of the process, so there seems littlereason not to cache this one as well.) This probably won't help much inprocesses that never run pg_timezone_names, but even one additional SETof the timezone GUC would come out ahead.An even worse problem for pg_timezone_names is that pg_open_tzfile()has an inefficient way of identifying the canonical case of a zone name:it basically re-descends the directory tree to the zone file. That's notawful for an individual "SET timezone" operation, but it's pretty horridwhen we're inspecting every zone in the database. And it's pointless toobecause we already know the canonical spelling, having just read it fromthe filesystem. Fix by teaching pg_open_tzfile() to avoid the directorysearch if it's not asked for the canonical name, and backfilling theproper result in pg_tzenumerate_next().In combination these changes seem to make the pg_timezone_names viewabout 3x faster to read, for me. Since a scan of pg_timezone_nameshas up to now been one of the slowest queries in the regression tests,this should help some little bit for buildfarm cycle times.Back-patch to all supported branches, not so much because it's likelythat users will care much about the view's performance as becausetracking changes in the upstream IANA timezone code is really painfulif we don't keep all the branches in sync.Discussion:https://postgr.es/m/27962.1493671706@sss.pgh.pa.us
1 parentd56b8b4 commitc521d5a

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3 files changed

+60
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lines changed

3 files changed

+60
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lines changed

‎src/timezone/README

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -79,6 +79,9 @@ other exposed names.
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slightly modified the API of the former, in part because it now relies
8080
on our own pg_open_tzfile() rather than opening files for itself.
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82+
* tzparse() is adjusted to cache the result of loading the TZDEFRULES
83+
zone, so that that's not repeated more than once per process.
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* There's a fair amount of code we don't need and have removed,
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including all the nonstandard optional APIs. We have also added
8487
a few functions of our own at the bottom of localtime.c.

‎src/timezone/localtime.c

Lines changed: 22 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -54,6 +54,13 @@ static const char gmt[] = "GMT";
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staticconstpg_time_ttime_t_min=MINVAL(pg_time_t,TYPE_BIT(pg_time_t));
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staticconstpg_time_ttime_t_max=MAXVAL(pg_time_t,TYPE_BIT(pg_time_t));
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/*
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* We cache the result of trying to load the TZDEFRULES zone here.
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* tzdefrules_loaded is 0 if not tried yet, +1 if good, -1 if failed.
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*/
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staticstructstatetzdefrules_s;
62+
staticinttzdefrules_loaded=0;
63+
5764
/*
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* The DST rules to use if TZ has no rules and we can't load TZDEFRULES.
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* We default to US rules as of 1999-08-17.
@@ -942,7 +949,21 @@ tzparse(const char *name, struct state * sp, bool lastditch)
942949
charcnt=stdlen+1;
943950
if (sizeofsp->chars<charcnt)
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return false;
945-
load_ok=tzload(TZDEFRULES,NULL,sp, false)==0;
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/*
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* This bit also differs from the IANA code, which doesn't make any
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* attempt to avoid repetitive loadings of the TZDEFRULES zone.
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*/
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if (tzdefrules_loaded==0)
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{
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if (tzload(TZDEFRULES,NULL,&tzdefrules_s, false)==0)
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tzdefrules_loaded=1;
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else
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tzdefrules_loaded=-1;
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}
964+
load_ok= (tzdefrules_loaded>0);
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if (load_ok)
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memcpy(sp,&tzdefrules_s,sizeof(structstate));
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}
947968
if (!load_ok)
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sp->leapcnt=0;/* so, we're off a little */

‎src/timezone/pgtz.c

Lines changed: 35 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -80,12 +80,37 @@ pg_open_tzfile(const char *name, char *canonname)
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intfullnamelen;
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intorignamelen;
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/* Initialize fullname with base name of tzdata directory */
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strlcpy(fullname,pg_TZDIR(),sizeof(fullname));
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orignamelen=fullnamelen=strlen(fullname);
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if (fullnamelen+1+strlen(name) >=MAXPGPATH)
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return-1;/* not gonna fit */
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/*
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* If the caller doesn't need the canonical spelling, first just try to
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* open the name as-is. This can be expected to succeed if the given name
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* is already case-correct, or if the filesystem is case-insensitive; and
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* we don't need to distinguish those situations if we aren't tasked with
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* reporting the canonical spelling.
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*/
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if (canonname==NULL)
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{
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intresult;
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fullname[fullnamelen]='/';
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/* test above ensured this will fit: */
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strcpy(fullname+fullnamelen+1,name);
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result=open(fullname,O_RDONLY |PG_BINARY,0);
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if (result >=0)
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returnresult;
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/* If that didn't work, fall through to do it the hard way */
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}
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/*
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* Loop to split the given name into directory levels; for each level,
85112
* search using scan_directory_ci().
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*/
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strlcpy(fullname,pg_TZDIR(),sizeof(fullname));
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orignamelen=fullnamelen=strlen(fullname);
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fname=name;
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for (;;)
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{
@@ -97,8 +122,6 @@ pg_open_tzfile(const char *name, char *canonname)
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fnamelen=slashptr-fname;
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else
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fnamelen=strlen(fname);
100-
if (fullnamelen+1+fnamelen >=MAXPGPATH)
101-
return-1;/* not gonna fit */
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if (!scan_directory_ci(fullname,fname,fnamelen,
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fullname+fullnamelen+1,
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MAXPGPATH-fullnamelen-1))
@@ -458,10 +481,11 @@ pg_tzenumerate_next(pg_tzenum *dir)
458481

459482
/*
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* Load this timezone using tzload() not pg_tzset(), so we don't fill
461-
* the cache
484+
* the cache. Also, don't ask for the canonical spelling: we already
485+
* know it, and pg_open_tzfile's way of finding it out is pretty
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* inefficient.
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*/
463-
if (tzload(fullname+dir->baselen,dir->tz.TZname,&dir->tz.state,
464-
true)!=0)
488+
if (tzload(fullname+dir->baselen,NULL,&dir->tz.state, true)!=0)
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{
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/* Zone could not be loaded, ignore it */
467491
continue;
@@ -473,6 +497,10 @@ pg_tzenumerate_next(pg_tzenum *dir)
473497
continue;
474498
}
475499

500+
/* OK, return the canonical zone name spelling. */
501+
strlcpy(dir->tz.TZname,fullname+dir->baselen,
502+
sizeof(dir->tz.TZname));
503+
476504
/* Timezone loaded OK. */
477505
return&dir->tz;
478506
}

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