Abstract: GaussDB (DWS) about time zone related knowledge and usage.
This article is shared from the HUAWEI CLOUD community " everyone knows the time zone, there are so many mysteries behind ", the original author: leapdb.
Background introduction
Time zone is the same as other industry standards, the standardization process is also a complicated and long process. GaussDB (DWS), as a high-performance analytical database product for global users, supports time zone is in line with industry standards. The following introduces GaussDB (DWS) from the concept of time zone, the usage and principle of GaussDB (DWS) time zone, and some common problems.
I hope it will be helpful for everyone to understand GaussDB (DWS) and time zone concepts.
Concept
In the past when countries all over the world were in an agricultural society, people determined the time by observing the position of the sun every day, which made places with different longitudes have different times. At that time, people traveled mainly by walking and horses, and the problem of time inconsistency in different places was not so prominent. But in the nineteenth century, with the invention of the train, the distance people traveled in a day has been extended a lot. Therefore, there is an urgent need for a universal method to unify the time in various places. On August 12, 1853, in Rhode Island, in the eastern United States, two trains collided head-on, causing 14 deaths. The cause of the accident seems unbelievable today-the watches of the engineers of the two cars are two minutes apart.
- In 1863, the concept of time zone was used for the first time. Time zones partially solve this problem by setting up a regional standard time.
- In the 1870s, Canadian Railway Engineer Fleming proposed for the first time that the world divides time zones according to uniform standards.
- On November 18, 1883, the U.S. Railway Department officially implemented five time zones.
- In 1884, the Washington Meridian International Conference formally adopted this time zone division, which is called the Universal Standard Time System. Therefore, the birth of the world standard time zone, like other global standards, has a slow development process.
1 Glossary
Time zone A time zone is defined by the same time used for the area on the earth. In the past, people determined the time by observing the position of the sun (hour angle), which made the time at different longitudes (local time) different. In 1863, the concept of time zone was used for the first time. Time zones partially solve this problem by setting up a regional standard time. Countries in the world are located in different locations on the earth, so different countries, especially countries with a large east-west span, must have different sunrise and sunset times. These deviations are the so-called jet lag.
GMT (Greenwich Mean Time) refers to the standard time of the Royal Greenwich Observatory located in the suburbs of London, England, because the prime meridian is defined as the longitude passing there. Due to the uneven speed of the earth in its elliptical orbit, the daily rotation of the earth is somewhat irregular, and it is slowly decelerating. Therefore, Greenwich Mean Time is no longer used as standard time.
UTC (Coordinated Universal Time) is a comprehensive actuarial calculation of the average solar time (based on Greenwich Mean Time GMT), the new time scale corrected for earth axis movement, and the International Atomic Time in "seconds". Time. UTC is more accurate than GMT. For the current models, there is no difference between the functions and accuracy of GMT and UTC.
Summer time saving DST (Daylight Saving Time) is also known as Daylight Saving Time, and it is called Summer Time in the UK. It is a system of artificially setting local time for energy conservation. The unified time adopted during the implementation of this system is called "daylight saving time". Generally, in the summer when the daylight is early, the time is artificially adjusted one hour forward, which can make people get up and go to bed early, reduce the amount of lighting, and make full use of light resources, thereby saving lighting power. National regulations that adopt daylight saving time are different.
time zone notation If the time is expressed in Coordinated Universal Time (UTC), add a "Z" directly after the time (without spaces). "Z" is the symbol of time zone 0 in Coordinated Universal Time. Therefore, "09:30 UTC" is written as "09:30Z" or "0930Z". "14:45:15 UTC" is "14:45:15Z" or "144515Z". UTC time is also called Zulu time because "Zulu" means "Z" in the NATO phonetic alphabet.
UTC offset UTC offset is the difference between Coordinated Universal Time (UTC) and the date and time of a specific location, in hours and minutes. It is usually displayed in the format of ±[hh]:[mm], ±hh, or ±[hh]. Therefore, if the time described is one hour earlier than UTC (for example, the winter time in Berlin), the offset from UTC will be "+01:00", "+0100", or simply displayed as "+01".
National time adjustment
- Morocco began to adjust the start time of daylight saving time from June 1 to May 2 in 2010, and the end time from August 21 to August 8.
- Tunisia has abandoned daylight saving time since 2010
- Macquarie Island is located between Australia and Antarctica. It was decided not to adopt daylight saving time along with other parts of Australia from April 4, 2010, resulting in a new time zone Antarctica/Macquarie, referred to as MIST
- North Korea-The time zone will be adjusted from May 5, 2018. The time zone is changed from GMT+8:30 to GMT+9:00. Therefore, Pyongyang’s standard time was changed to 00:00:00 on Saturday, May 5, 2018: 00:00:00 30:00 dial 30 minutes forward. When Greenwich Mean GMT standard time is 0:00 am, Pyongyang time is 9:00 am, which is the same time zone as South Korea and Japan.
- North Korea-Starting from August 15, 2015, GMT+9 will be abandoned, and the GMT+8:30 standard time of the Korean Empire will be "restored". The newly activated time is 30 minutes slower than the original time, and it is the only one in use in the world Country in this time zone. When Greenwich Mean GMT is 0:00 in the morning, Pyongyang time is 8:30 in the morning.
- Chile-On January 28, 2015, Chile adopted a new official standard time. They merged the original standard time and daylight saving time into one, permanently adopting the daylight saving time system. The new official time is GMT-3 on the Chilean mainland and GMT-5 on Easter Island.
- Russia-The last Sunday of October 2014 (October 26, 2014) will start in the early hours of the morning, and the winter time system will be permanently adopted, and the country will be delayed by one hour. Therefore, Moscow time will be changed from GMT+4 to GMT+3.
It can be seen that both the time zone and daylight saving time will often change.
2 Universal time format
Mainly refer to Posix 1003.1 Section 8.3. The TZ environment variable in the operating system represents time zone information, and is mainly used for ctime, localtime, mktime, and so on. The TZ time zone name has two forms: the time zone name format and the POSIX time zone format.
2.1 Time zone name format
:characters This form starts with a colon, and the subsequent character processing is implementation-dependent. On linux, it means to read time zone information from a file, such as TZ=":Pacific/Auckland".
2.2 POSIX time zone format
Formats that do not start with a colon are counted as this format, and are expanded as follows. The field representation in [] is optional: std offsetdst[offset, enddate[/time]]]
Format: std offset[dst[offset][,startdate[/time], enddate[/time]]]
The meaning of each field is as follows:
- std && dst stands for standard time zone and daylight saving time zone, std is required, dst is optional (dst field means support for daylight saving time). There are two formats for these two fields:
- a. A quotation symbol <>, the string in the quotation symbol can be letters, numbers, +, -, and does not include the quotation symbol <> when parsed;
- b. The other is without reference symbol <>, the string can only be letters.
The field length is greater than or equal to 3 and less than or equal to TZNAME_MAX (Linux is 6). If the length of the string does not meet the requirements, the parsing rules are not defined (Linux does not recognize).
- The offset represents the UTC time by adding the local time.
The format is hh[:mm[:ss]], 0<=hh<=24, 0<=mm&&ss<=59. hh is required and can be 1 digit, mm and ss are optional.
- If there is a plus sign + in front, it means west of the prime meridian. Indicates how much time is added to this time to get UTC time. The plus sign can also be omitted.
- If there is a minus sign in front of it, it means east of the prime meridian. Indicates how much time is subtracted from this time to get UTC time.
The offset after std is required, and the offset after dst is optional. If not, the default is one hour ahead of standard time.
- The rule indicates when the daylight saving time starts and when the daylight saving time ends. The agreement does not mention how to deal with the situation where there is no rule. From the Linux system, if there is no rule, the default is M3.2.0/02:00:00, M11.1.0/02 :00:00 processing.
The format is date[/time],date[/time]. There are three forms of date:
a. Jn, 1 <= n <= 365, excluding February 29 of a leap year;
b. n, 0 <= n <= 365, including February 29 of a leap year;
c. Mm.nd, m represents the month (1 <= m <= 12), n represents the week of the month (1 <= n <= 5), 5 represents the last one, and d represents the day of the week (0 <= d <= 6, starting from Sunday).
- The time format is the same as the offset, except that there is no + and -. If there is no time field, the default is 02:00:00.
Example: "UTC-8:00:00DST-09:00:00,M3.2.0/02:00:00,M11.1.0/02:00:00"
Indicates that the local time is east of UTC minus 8 hours, supports daylight saving time and summer time is UTC minus 9 hours (and one hour ahead). Daylight saving time starts at 2 a.m. on the 0th day of the second week of March and ends on the 1st of November It ends at 2 am on the 0th day of the week.
CST6CDT,M3.2.0/2:00:00,M11.1.0/2:00:00
The POSIX time zone format has not been widely adopted because it cannot represent times that do not use the Gregorian calendar (such as Greece).
3 Universal time zone database
The local time zone and daylight saving time rules are independently managed by their respective governments, and they often change with limited notice. Moreover, their historical data and future plans are only intermittently recorded. The Universal Time Zone Database attempts to organize and organize relevant data in this field.
The time zone database, usually called tz, tzdata or zoneinfo, is a set of historical information containing a large number of codes and data used to represent the local time of many representative locations around the world. It will determine the time zone boundaries and daylight saving time rules of each government Change and update from time to time. Each entry in the database represents the time zone information of this widely recognized civilian clock since 1970. The database is referenced by many projects, such as: the GNU C Library (used in GNU/Linux), Android, FreeBSD, NetBSD, OpenBSD, Chromium OS, Cygwin, MariaDB, MINIX, MySQL, webOS, AIX, BlackBerry 10, iOS, macOS , Microsoft Windows, OpenVMS, Oracle Database, and Oracle Solaris. GaussDB, like other widely used software products, also uses universal time zone data maintained by IANA.
The database was founded by David Olson and edited and maintained by Paul Eggert. Therefore, it is also called Olson database in some places. Its notable feature is a set of universal time zone naming rules designed by Paul Eggert. Each time zone is given a unique name in the format of "area/location", such as "America/New_York". The space in the English place name is replaced with an underscore "_", and the conjunction "-" is only used when the English place name itself is included. Time zone databases are currently generally called Olson time zone database or IANA time zone database.
Olson's data has changed, partly because of the imminent retirement of AD Olson, and partly because of a lawsuit (now revoked) against defenders for copyright infringement. On October 14, 2011, the Internet Corporation for Assigned Names and Names (IANA) took over the maintenance of the time zone database. It is regularly updated to reflect changes to time zone boundaries, UTC differences, and daylight saving time rules by various political entities. Updates to tz are managed in accordance with the BCP 175 process. Some countries often change their time zone rules. IANA releases the latest time zone data and parsing source code libraries every year.
In fact, how to define and manage time zones is a controversial matter, and there is no absolutely authoritative time zone database. The universal time zone database maintained by IANA is widely used because each record identifies a clear source of information, and it is possible to speculate the future time with historical information. It is widely used by the GNU C Library and BSD. In fact, there are other time zone databases, such as: Microsoft time zone database, HP-UX time zone database, world time server ( https://www.worldtimeserver.com/) and International Air Transport Association's "Standard Timetable Information Manual", etc. .
Practical articles
1 The use of GaussDB (DWS) time zone
The system table pg_timezone_names records time zone names.
testdb=# select * from pg_timezone_names where utc_offset='08:00:00';
name | abbrev | utc_offset | is_dst
--------------------+--------+------------+--------
Asia/Kuala_Lumpur | +08 | 08:00:00 | f
Asia/Brunei | +08 | 08:00:00 | f
Asia/Makassar | WITA | 08:00:00 | f
Asia/Harbin | CST | 08:00:00 | f
Asia/Ujung_Pandang | WITA | 08:00:00 | f
Asia/Chungking | CST | 08:00:00 | f
Asia/Kuching | +08 | 08:00:00 | f
Asia/Taipei | CST | 08:00:00 | f
Asia/Macau | CST | 08:00:00 | f
Asia/Macao | CST | 08:00:00 | f
Asia/Manila | PST | 08:00:00 | f
Asia/Chongqing | CST | 08:00:00 | f
Asia/Shanghai | CST | 08:00:00 | f
Asia/Choibalsan | +08 | 08:00:00 | f
Asia/Ulaanbaatar | +08 | 08:00:00 | f
Asia/Irkutsk | +08 | 08:00:00 | f
Asia/Ulan_Bator | +08 | 08:00:00 | f
Asia/Hong_Kong | HKT | 08:00:00 | f
Asia/Singapore | +08 | 08:00:00 | f
Australia/West | AWST | 08:00:00 | f
Australia/Perth | AWST | 08:00:00 | f
ROC | CST | 08:00:00 | f
Etc/GMT-8 | +08 | 08:00:00 | f
PRC | CST | 08:00:00 | f
Singapore | +08 | 08:00:00 | f
Antarctica/Casey | +08 | 08:00:00 | f
Hongkong | HKT | 08:00:00 | f
(27 rows)The system table pg_timezone_abbrevs records the abbreviation of the time zone
testdb=# select * from pg_timezone_abbrevs where utc_offset='08:00:00';
abbrev | utc_offset | is_dst
--------+------------+--------
AWST | 08:00:00 | f
BNT | 08:00:00 | f
BORT | 08:00:00 | f
CCT | 08:00:00 | f
HKT | 08:00:00 | f
IRKST | 08:00:00 | f
IRKT | 08:00:00 | f
MYT | 08:00:00 | f
PHT | 08:00:00 | f
SGT | 08:00:00 | f
ULAT | 08:00:00 | f
WADT | 08:00:00 | t
(12 rows)You can set the time zone for database data storage and query by setting the session environment variable timezone. Why is it session level? What if the user does not need to set a different time zone, or the user forgets the time zone previously set?
Answer: After the time data is stored in the database, the background of the database management software will convert the time to UTC 0 time zone time. When the user queries, it will be converted to the corresponding time for the user according to the time zone set by the user. Therefore, the time zone set by the user does not affect data storage, and there is no need to care about the time zone during data migration.
2 How to set the default time zone when GaussDB (DWS) is initialized
If the time zone is not specified in the configuration file, the current operating system time zone will be obtained from the current operating system environment variable TZ, and if the time zone is a time zone supported in the database, the operating system time zone will be used directly. Otherwise, construct some dates based on the current time of the operating system to judge which time zone is more compatible with the operating system.
Judging method:
1) Collect some time stamps within 100 years from now on
First, detect January and July of the current year, which can quickly eliminate a large number of non-compliant time zones.
Secondly, detecting the weekly period from July of the current year to the next 100 years can effectively eliminate time zones that do not comply with daylight saving time.
tnow = time(NULL); //获取1970-01-01 00:00:00 UTC至今所经历过的秒数
tm_val = localtime(&tnow); //将从time()获取的时间戳，转为本地时间的tm结构格式
thisyear = tm_val->tm_year + 1900; //tm_year是自1900年起的年数，所以要加1900
time_needto_test = 0;
//先构造一个当年的1月15日，再调整到当前周的第一天 00:00:00
t = MakeTime(thisyear, 1, 15);
t -= (t % T_WEEK);
test_times[time_needto_test++] = t;
//构造一个当年的7月15日，再调整到当前周的第一天 00:00:00
t = MakeTime(thisyear, 7, 15);
t -= (t % T_WEEK);
test_times[time_needto_test++] = t;
//构造向后100年内每周的时间
while (tt.n_test_times < 52 * 100) {
t -= T_WEEK;
test_times[time_needto_test++] = t;
}
//总共构造了5202个探测时间2) Determine the degree of matching between the internal time zone of each database and the operating system time zone
If a timestamp is converted to the operating system time zone and the time after the conversion to the internal time zone of the database to be tested is consistent, one point is added. When a mismatch is encountered, the current time zone matching is ended.
First, determine the degree of match between the time zone in "/etc/localtime" and the previous test time, and return success if it matches exactly.
Otherwise, determine the matching degree of each time zone file under the database installation directory timezone with the previous test time, and obtain the time zone with the highest matching degree.
bestscore = 0；
for (获取每一个时区文件) {
判断当前时区文件与探测时间的匹配度
score = score_timezone(tzdirsub, tt);
if (score > bestscore) { //当前时区文件匹配度 > 目前最大匹配度
bestscore = score;
bestzonename = tzdirsub;
} else if (score == bestscore) { //如果当前时区文件匹配度与目前最大匹配度相等，则选择长度更短，字母排序更靠前的时区
if ((strlen(tzdirsub) < strlen(bestzonename) ||
(strlen(tzdirsub) == strlen(bestzonename) && strcmp(tzdirsub, bestzonename) < 0))
strlcpy(bestzonename, tzdirsub, TZ_STRLEN_MAX + 1);
}
}3) If the internal time zones of all databases are matched and the best score is still 0, a POSIX style time zone that is consistent with the operating system time zone needs to be constructed, for example: "PSD8PDT"
Cold Knowledge
1 What time zones are there in my country and how are they set?
Before 1912, there was no uniform standard time in all parts of China. In the feudal era, the country’s standard calendar was promulgated by the imperial court, while the traditional Chinese calendar relied on the movement of the sun and the moon at the same time and was based on actual astronomical observations. Therefore, the diachronic standards were based on the imperial court’s location (to be precise, Qin Tian The longitude and latitude of the monitoring point) shall prevail.
In 1912, the Republic of China was established, and the time zone division was first established and officially promulgated to divide China into five time zones, which were officially promulgated in 1939.
1: Kunlun Time Zone (GMT+5:30)
2: Xinzang time zone (GMT+6)
3: Longshu time zone (GMT+7)
4: Central Plains Standard Time Zone (GMT+8)
5: Changbai time zone (GMT+8:30)
The details are as follows:
Asia/Harbin is also called Changbai time zone, which mainly represents Heilongjiang (excluding Mohe) and the time in Jilin area
# Zone NAME GMTOFF RULES FORMAT [UNTIL]
# Changbai Time ("Long-white Time", Long-white = Heilongjiang area)
# Heilongjiang (except Mohe county), Jilin
Zone Asia/Harbin 8:26:44 - LMT 1928 # or Haerbin
8:30 - CHAT 1932 Mar # Changbai Time
8:00 - CST 1940
9:00 - CHAT 1966 May
8:30 - CHAT 1980 May
8:00 PRC C%sTAsia/Shanghai is also called the Central Plains Standard Time Zone
# Zhongyuan Time ("Central plain Time")
# most of China
# Milne gives 8:05:56.7; round to nearest.
Zone Asia/Shanghai 8:05:57 - LMT 1928
8:00 Shang C%sT 1949
8:00 PRC C%sTAsia/Chongqing is also called the Shu time zone, which mainly represents Guangxi, Guizhou, Hainan, Ningxia, Sichuan, Shaanxi, Yunnan, main parts of Gansu, western Inner Mongolia, western Qinghai, Deqing, Enping, Kaiping, Luoding, Taishan in Guangdong , Xinxing, Yangchun, Yangjiang, Yunan, Yunfu are the Seventh District of the East.
# Long-shu Time (probably due to Long and Shu being two names of that area)
# Guangxi, Guizhou, Hainan, Ningxia, Sichuan, Shaanxi, and Yunnan;
# most of Gansu; west Inner Mongolia; west Qinghai; and the Guangdong
# counties Deqing, Enping, Kaiping, Luoding, Taishan, Xinxing,
# Yangchun, Yangjiang, Yu'nan, and Yunfu.
Zone Asia/Chongqing 7:06:20 - LMT 1928 # or Chungking
7:00 - LONT 1980 May # Long-shu Time
8:00 PRC C%sTAsia/Urumqi is also called Xinzang time zone, which mainly represents Aksaiha Autonomous County, Anxi County, Dunhuang, Subei County, Lianjiang County, Zhanjiang City, etc. in Gansu.
# Xin-zang Time ("Xinjiang-Tibet Time")
# The Gansu counties Aksay, Anxi, Dunhuang, Subei; west Qinghai;
# the Guangdong counties Xuwen, Haikang, Suixi, Lianjiang,
# Zhanjiang, Wuchuan, Huazhou, Gaozhou, Maoming, Dianbai, and Xinyi;
# east Tibet, including Lhasa, Chamdo, Shigaise, Jimsar, Shawan and Hutubi;
# east Xinjiang, including Urumqi, Turpan, Karamay, Korla, Minfeng, Jinghe,
# Wusu, Qiemo, Xinyan, Wulanwusu, Jinghe, Yumin, Tacheng, Tuoli, Emin,
# Shihezi, Changji, Yanqi, Heshuo, Tuokexun, Tulufan, Shanshan, Hami,
# Fukang, Kuitun, Kumukuli, Miquan, Qitai, and Turfan.
Zone Asia/Urumqi 5:50:20 - LMT 1928 # or Urumchi
6:00 - URUT 1980 May # Urumqi Time
8:00 PRC C%sTAsia/Kashgar is also called Kunlun Time Zone, which mainly represents western Tibet (Pulan County, Aheqi County, Shufu County, Shule County) and western Xinjiang (Aksu, Atushi, Yining, Hotan, Cele, Luopu) , Nilek, Zhaosu, Turks, Gongliu, Chabucar, Huocheng, Bole, Pishan, etc.)
Zone Asia/Kashgar 5:03:56 - LMT 1928 # or Kashi or Kaxgar
5:30 - KAST 1940 # Kashgar Time
5:00 - KAST 1980 May
8:00 PRC C%sTPRC points to the Central Plains Standard Time Zone
Link Asia/Shanghai PRC
The People’s Republic of China was established in 1949. my country abolished the Central Plains Standard Time Zone, Kunlun Time Zone, Changbai Time Zone, Longshu Time Zone, and Xinzang Time Zone established in 1939 by the original National Government. It is used uniformly across the country (UTC+8) and named Beijing Time .
After 1950, Beijing time was used uniformly across the country except Tibet and Xinjiang. At that time, the local people's congress in Xinjiang set the Urumqi time for the convenience of the masses: (UTC+6), such as 8 o'clock in Beijing time and 6 o'clock in Urumqi time. The new time zone adjustments are as follows:
1) Asia/Harbin (Changbai time zone), Asia/Chongqing (Longshu time zone), Asia/Shanghai (Central Plains standard time zone) time zone names are reserved, and the definitions all point to the newly defined Asia/Shanghai (Chinese standard time zone). Used uniformly throughout the country.
The Central Plains Standard Time Zone was renamed Beijing Time Zone, and the offset was adjusted
# Zone NAME STDOFF RULES FORMAT [UNTIL]
# Beijing time, used throughout China; represented by Shanghai.
Zone Asia/Shanghai 8:05:43 - LMT 1901
8:00 Shang C%sT 1949 May 28
8:00 PRC C%sT2) Asia/Kashgar (Kunlun time zone), Asia/Urumqi (Xinzang time zone) time zone names are reserved, and the definitions all point to the newly defined Asia/Urumqi (Urumqi time zone). Two local time zone definitions are used at the same time.
The new Tibet time zone was renamed as the Xinjiang time zone offset adjustment
# Xinjiang time, used by many in western China; represented by Ürümqi / Ürümchi
# / Wulumuqi. (Please use Asia/Shanghai if you prefer Beijing time.)
Zone Asia/Urumqi 5:50:20 - LMT 1928
6:00 - +06Merged time zone
L Asia/Urumqi Asia/Kashgar 昆仑时区合入新藏时区
L Asia/Shanghai Asia/Harbin 长白时区合入中原标准时区
L Asia/Shanghai Asia/Chongqing 胧蜀时区合入中原标准时区
L Asia/Shanghai Asia/Chungking 胧蜀时区新增别名Chungking，也合入中原标准时区
L Asia/Shanghai PRC2 Why is there no Beijing time zone and only Beijing time?
Due to various political reasons, the country where the country is located, the name of the country and the country to which the region belongs will change from time to time, which brings a lot of trouble to time zone management. For example: The "Kingdom of Swaziland", a landlocked country located in southeastern Africa, announced in April 2018 that the country name was changed to "Eswatini"; on July 1, 1997, Hong Kong, which we are absolutely familiar with, was from the British The colony returned to the embrace of our great motherland, and the country to which it belonged was changed. Therefore, IANA’s strategy is to remain neutral to political changes. Time zones are usually not tied to countries, and it does not require that every country or national capital must have a time zone name.
For the convenience of domestic users, GaussDB (DWS) internally helps users define the Asia/Beijing time zone according to the grammatical rules defined by IANA, and its definition is consistent with the PRC time zone definition.
3 Is the time zone definition set in stone?
How to define and manage time zones is a controversial matter, and there is no absolutely authoritative time zone database. The time zone information change of a country or region is an independent matter, and there is no obligation to notify IANA. The authority of the IANA time zone database mainly depends on the knowledge of the time zone database maintainer about the relevant country or region.
Therefore, the time zone definition of IANA records the source of time zone information collected by the time zone database maintainer, which is sometimes not very objective. The following is the reference basis for my country's time zone information in IANA.
From Guy Harris:
From Bob Devine (1988-01-28): See TIME mag, 1986-02-17 p.52.
From U. S. Naval Observatory (1989-01-19):
From Anthony Fok (2001-12-20): from some Taiwan websites
From Paul Eggert (2006-03-22): Devine's note about Time magazine
From Jesper Norgaard Welen (2006-07-14): http://www.astro.com/atlas
From Paul Eggert (2008-02-11): I just now checked Google News for western news sources
From David Cochrane (2014-03-26): https://content.time.com/time/magazine/article/0,9171,960684,00.html
From Luther Ma (2014-04-22): Guo's report regarding Xinjiang
From Paul Eggert (2014-06-30): http://www.sinkiang.gov.cn/service/ourworking (2014-04-22).
From Paul Eggert (2017-01-05):
Guo Qing-sheng (National Time-Service Center, CAS, Xi'an 710600, China)
(Zhongguo ke ji shi liao, 中国科技史料). 2003;24(1):5-9.
http://oversea.cnki.net/kcms/detail/detail.aspx?filename=ZGKS200301000&dbname=CJFD2003
Guo Qing-sheng (Shaanxi Astronomical Observatory, CAS, Xi'an 710600, China)
An AP article "Shanghai Internat'l Area Little Changed"
From P Chan (2018-05-07):
1986-04-12 http://www.zj.gov.cn/attach/zfgb/198608.pdf p.21-22
1987-02-15 http://www.gov.cn/gongbao/shuju/1987/gwyb198703.pdf p.114
1987-09-09 http://www.gov.cn/gongbao/shuju/1987/gwyb198721.pdf p.709
1992-03-03 http://www.gov.cn/gongbao/shuju/1992/gwyb199205.pdf p.152
http://data.people.com.cn/pic/101p/1988/04/1988041201.jpgIt can be seen that before 2014, most of the sources for IANA to collect China's time zone information were Western news, magazines, Taiwanese websites, and so on. The information collected after 2014 comes from China's Xi'an Time Service Center, the national portal website, etc.
In addition, because the time zone information of many countries changes frequently, the time zone data in the IANA common time zone database will be updated frequently. GaussDB (DWS), as a universal database product facing the world, will also synchronize the latest time zone information from IANA every time a new version is released to ensure that users' software products maintain the latest time zone information.
4 Why do we rarely need to pay attention to time zone?
Since the cancellation of daylight saving time in 1992, our time zone information has never been changed, which has brought great convenience to our production and life. Domestic users no longer need to care about time zone related issues.
to sum up
In summary, GaussDB (DWS), as a high-performance analytical database product for global users, also supports time zones in compliance with industry standards. The time zone in GaussDB (DWS) is simple and convenient to use, and the default time zone selection is also scientific and reasonable.
For more information about GuassDB (DWS), welcome to search "GaussDB DWS" on WeChat and follow the WeChat official account to share with you the latest and most complete PB-level data warehouse black technology~
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