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Cache the result of converting now() to a struct pg_tm.

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SQL operations such as CURRENT_DATE, CURRENT_TIME, LOCALTIME, and
conversion of "now" in a datetime input string have to obtain the
transaction start timestamp ("now()") as a broken-down struct pg_tm.
This is a remarkably expensive conversion, and since now() does not
change intra-transaction, it doesn't really need to be done more than
once per transaction.  Introducing a simple cache provides visible
speedups in queries that compute these values many times, for example
insertion of many rows that use a default value of CURRENT_DATE.

Peter Smith, with a bit of kibitzing by me

Discussion: https://postgr.es/m/CAHut+Pu89TWjq530V2gY5O6SWi=OEJMQ_VHMt8bdZB_9JFna5A@mail.gmail.com
This commit is contained in:
Tom Lane
2020-09-28 12:05:03 -04:00
parent e21cbb4b89
commit 0a87ddff5c
2 changed files with 80 additions and 36 deletions
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49
src/backend/utils/adt/date.c
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@@ -299,20 +299,31 @@ EncodeSpecialDate(DateADT dt, char *str)
DateADT
GetSQLCurrentDate(void)
{
TimestampTz ts;
struct pg_tm tt,
*tm = &tt;
fsec_t fsec;
int tz;
struct pg_tm tm;
ts = GetCurrentTransactionStartTimestamp();
static int cache_year = 0;
static int cache_mon = 0;
static int cache_mday = 0;
static DateADT cache_date;
if (timestamp2tm(ts, &tz, tm, &fsec, NULL, NULL) != 0)
ereport(ERROR,
(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
errmsg("timestamp out of range")));
GetCurrentDateTime(&tm);
return date2j(tm->tm_year, tm->tm_mon, tm->tm_mday) - POSTGRES_EPOCH_JDATE;
/*
* date2j involves several integer divisions; moreover, unless our session
* lives across local midnight, we don't really have to do it more than
* once. So it seems worth having a separate cache here.
*/
if (tm.tm_year != cache_year ||
tm.tm_mon != cache_mon ||
tm.tm_mday != cache_mday)
{
cache_date = date2j(tm.tm_year, tm.tm_mon, tm.tm_mday) - POSTGRES_EPOCH_JDATE;
cache_year = tm.tm_year;
cache_mon = tm.tm_mon;
cache_mday = tm.tm_mday;
}
return cache_date;
}
/*
@@ -322,18 +333,12 @@ TimeTzADT *
GetSQLCurrentTime(int32 typmod)
{
TimeTzADT *result;
TimestampTz ts;
struct pg_tm tt,
*tm = &tt;
fsec_t fsec;
int tz;
ts = GetCurrentTransactionStartTimestamp();
if (timestamp2tm(ts, &tz, tm, &fsec, NULL, NULL) != 0)
ereport(ERROR,
(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
errmsg("timestamp out of range")));
GetCurrentTimeUsec(tm, &fsec, &tz);
result = (TimeTzADT *) palloc(sizeof(TimeTzADT));
tm2timetz(tm, fsec, tz, result);
@@ -348,18 +353,12 @@ TimeADT
GetSQLLocalTime(int32 typmod)
{
TimeADT result;
TimestampTz ts;
struct pg_tm tt,
*tm = &tt;
fsec_t fsec;
int tz;
ts = GetCurrentTransactionStartTimestamp();
if (timestamp2tm(ts, &tz, tm, &fsec, NULL, NULL) != 0)
ereport(ERROR,
(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
errmsg("timestamp out of range")));
GetCurrentTimeUsec(tm, &fsec, &tz);
tm2time(tm, fsec, &result);
AdjustTimeForTypmod(&result, typmod);