>From 337f1e4894bf7071c6d0c24a77c433a0b9e0cc81 Mon Sep 17 00:00:00 2001 From: Craig Ringer Date: Fri, 12 Sep 2014 12:41:35 +0800 Subject: [PATCH 1/2] Use GetSystemTimeAsFileTime directly in windows gettimeofday MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit PostgreSQL was calling GetSystemTime followed by SystemTimeToFileTime in the win32 port gettimeofday function. This is not necessary and limits the reported precision to the 1ms granularity that the SYSTEMTIME struct can represent. By using GetSystemTimeAsFileTime we avoid unnecessary conversions and capture timestamps at 100ns granularity, which is then rounded to 1µs granularity for storage in a PostgreSQL timestamp. On most Windows systems this change will actually have no significant effect as the system timer tick is typically between 1ms and 15ms depending on what timer resolution currently running applications have requested. You can check this with clockres.exe from sysinternals. Despite the platform limiation this change still permits capture of finer timestamps where the system is capable of producing them and it gets rid of an unnecessary syscall. Future work may permit use of GetSystemTimePreciseAsFileTime on Windows 8 and Windows Server 2012 for higher resolution time capture. This call has the same interface as GetSystemTimeAsFileTime. --- src/port/gettimeofday.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/src/port/gettimeofday.c b/src/port/gettimeofday.c index 75a9199..73ec406 100644 --- a/src/port/gettimeofday.c +++ b/src/port/gettimeofday.c @@ -44,16 +44,14 @@ int gettimeofday(struct timeval * tp, struct timezone * tzp) { FILETIME file_time; - SYSTEMTIME system_time; ULARGE_INTEGER ularge; - GetSystemTime(&system_time); - SystemTimeToFileTime(&system_time, &file_time); + GetSystemTimeAsFileTime(&file_time); ularge.LowPart = file_time.dwLowDateTime; ularge.HighPart = file_time.dwHighDateTime; tp->tv_sec = (long) ((ularge.QuadPart - epoch) / 10000000L); - tp->tv_usec = (long) (system_time.wMilliseconds * 1000); + tp->tv_usec = (long) (((ularge.QuadPart - epoch) % 10000000L) / 10); return 0; } -- 1.9.3