Hi all
Attached is a patch to switch 9.5 over to using the
GetSystemTimeAsFileTime call instead of separate GetSystemTime and
SystemTimeToFileTime calls.
This patch the first step in improving PostgreSQL's support for Windows
high(er) resolution time.
In addition to requiring one less call into the platform libraries, this
change permits capture of timestamps at up to 100ns precision, instead
of the current 1ms limit. Unfortunately due to platform timer resolution
limitations it will in practice only report with 1ms resolution and
0.1ms precision - or sometimes even as much as 15ms resolution. (If you
want to know more, see the README for
https://github.com/2ndQuadrant/pg_sysdatetime).
On Windows 2012 and Windows 8 I'd like to use the new
GetSystemTimePreciseAsFileTime call instead. As this requires some extra
hoop-jumping to safely and efficiently use it without breaking support
for older platforms I suggest that we start with just switching over to
GetSystemTimeAsFileTime, which has been supported since Windows 2000.
Then more precise time capture can be added in a later patch.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
>From 337f1e4894bf7071c6d0c24a77c433a0b9e0cc81 Mon Sep 17 00:00:00 2001
From: Craig Ringer <cr...@2ndquadrant.com>
Date: Fri, 12 Sep 2014 12:41:35 +0800
Subject: [PATCH] Use GetSystemTimeAsFileTime directly in windows gettimeofday
MIME-Version: 1.0
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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
--
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