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[10] [DFN[leap smear]] は、[[閏秒]]の実施時に、周囲の各[[秒]]の長さを調整することで見かけの[[閏秒]]をなくすものです。
比較的正確に[[時刻同期]]されたシステムと[[閏秒のない時刻系]]の両立手法として広く用いられています。

[1] [CITE@en[Leap Second Smearing with NTP=]]
([TIME[2016-12-05 04:37:06 +09:00]])
<https://docs.ntpsec.org/latest/leapsmear.html>

[FIG(quote)[
[FIGCAPTION[
[2] [CITE@en[Google Cloud Platform Blog: Making every (leap) second count with our new public NTP servers]]
([TIME[2016-12-04 23:16:23 +09:00]])
<https://cloudplatform.googleblog.com/2016/11/making-every-leap-second-count-with-our-new-public-NTP-servers.html>
]FIGCAPTION]

> No commonly used operating system is able to handle a minute with 61 seconds, and trying to special-case the leap second has caused many problems in the past. Instead of adding a single extra second to the end of the day, we'll run the clocks 0.0014% slower across the ten hours before and ten hours after the leap second, and “smear” the extra second across these twenty hours. For timekeeping purposes, December 31 will seem like any other day.
> All Google services, including all APIs, will be synchronized on smeared time, as described above. You’ll also get smeared time for virtual machines on Compute Engine if you follow our recommended settings. You can use non-Google NTP servers if you don’t want your instances to use the leap smear, but don’t mix smearing and non-smearing time servers.

]FIG]

[FIG(quote)[
[FIGCAPTION[
[3] [CITE@en[Leap Smear  |  Public NTP  |  Google Developers]]
([TIME[2016-12-01 04:14:26 +09:00]])
<https://developers.google.com/time/smear>
]FIGCAPTION]

> Since 2008, instead of applying leap seconds to our servers using clock steps, we have "smeared" the extra second across the hours before and after each leap. The leap smear applies to all Google services, including all our APIs.

]FIG]

[FIG(quote)[
[FIGCAPTION[
[4] [CITE@en[Leap Smear  |  Public NTP  |  Google Developers]]
([TIME[2016-12-01 04:14:26 +09:00]])
<https://developers.google.com/time/smear>
]FIGCAPTION]

> Several other smears have been proposed or implemented.
> UTC-SLS is a linear smear over 1,000 s before the leap (23:43:20 to 00:00:00).
> Google's 2008 smear was a 20-hour cosine smear before the leap (04:00:00 to 00:00:00). We used a cosine smear only for leap #34.
> Bloomberg's smear is a linear smear over 2,000 s after the leap (00:00:00 to 00:33:20).
> Amazon, Microsoft, and Akamai have implemented 24-hour smears.

]FIG]

[FIG(quote)[
[FIGCAPTION[
[5] [CITE@en[Official Google Blog: Time, technology and leaping seconds]]
([TIME[2016-12-04 22:33:04 +09:00]])
<https://googleblog.blogspot.jp/2011/09/time-technology-and-leaping-seconds.html>
]FIGCAPTION]

> The solution we came up with came to be known as the “leap smear.” We modified our internal NTP servers to gradually add a couple of milliseconds to every update, varying over a time window before the moment when the leap second actually happens.

]FIG]

[6] [CITE@en[* Makefile, NEWS, tz-link.htm: Mention leap smearing.]]
([[eggert]]著, [TIME[2016-12-03 02:32:14 +09:00]])
<https://github.com/eggert/tz/commit/42df6286d5f5a44dbf2f89eb9dc84697310a257a>

[7] [CITE@en[draft-kuhn-leapsecond-00 - Coordinated Universal Time with Smoothed Leap Seconds (UTC-SLS)]] ([TIME[2017-02-13 00:36:57 +09:00]]) <https://tools.ietf.org/html/draft-kuhn-leapsecond-00>

[8] [CITE@en[UTC with Smoothed Leap Seconds (UTC-SLS)]]
([TIME[2017-01-03 00:17:49 +09:00]])
<http://www.cl.cam.ac.uk/~mgk25/time/utc-sls/>

[9] [CITE[Time::UTC_SLS - search.cpan.org]]
([TIME[2017-02-13 00:43:44 +09:00]])
<http://search.cpan.org/dist/Time-UTC_SLS/lib/Time/UTC_SLS.pm>

[FIG(quote)[
[FIGCAPTION[
[74] [CITE@ja-JP[事前にご確認ください – AWSにおける2016年12月31日(日本時間2017年1月1日)のうるう秒 | Amazon Web Services ブログ]]
( ([TIME[2016-12-24 11:31:29 +09:00]]))
<https://aws.amazon.com/jp/blogs/news/look-before-you-leap-december-31-2016-leap-second-on-aws/>
]FIGCAPTION]

> AWS調整時刻(AWS Adjusted Time) –うるう秒挿入前後の24時間の期間にわたって、うるう秒の1秒を少しずつ分散します(UTCで12月31日の11:59:59から、2017年1月1日12:00:00まで)。AWS調整時刻と協定世界時はこの期間が終了後に同期します。(訳注:この期間の1秒をごくわずかに遅くすることで、追加される1秒を長い時間のなかに分散する方法であり、これは前回うるう秒挿入時と同じ挙動です。詳しくは前回の情報をご確認ください。)
> Microsoft Windows – Amazonによって提供されたMicrosoft WindowsのAMIを利用しているインスタンスは、AWS調整時刻に従います。
> Amazon RDS – 大多数のAmazon RDS インスタンスは (UTCで設定されている場合)“23:59:59” を2回記録します。しかし、Oracle 11.2.0.2、11.2.0.3、12.1.0.1 はAWS調整時刻に従います。Oracle 11.2.0.4と12.1.0.2について詳細な情報が必要な場合はAWSサポートにお問い合わせください。

]FIG]

[11] [CITE['''['''tz''']''' What's "right"?]]
([TIME[2020-11-16T23:31:53.000Z]], [TIME[2020-11-17T00:48:14.043Z]])
<https://mm.icann.org/pipermail/tz/2020-November/029485.html>

[12] [CITE[Bloomberg-Leap-Second_December-2016.pdf]], [TIME[2016-09-16T16:33:11.000Z]], [TIME[2020-11-17T00:49:18.125Z]] <https://data.bloomberglp.com/professional/sites/4/Bloomberg-Leap-Second_December-2016.pdf>

[13] [CITE[Leap Second Smearing With NTP.pdf]], [TIME[2016-11-18T07:59:35.000Z]], [TIME[2020-11-17T00:52:17.956Z]] <https://www.meinbergglobal.com/download/burnicki/Leap%20Second%20Smearing%20With%20NTP.pdf>

[14] [CITE@en[Google Cloud Platform Blog: Got a second? A leap second that is. Be ready for June 30th!]], [TIME[2020-03-02T09:17:32.000Z]], [TIME[2020-11-17T01:12:36.768Z]] <https://cloudplatform.googleblog.com/2015/05/Got-a-second-A-leap-second-that-is-Be-ready-for-June-30th.html>

[15] [CITE[Leap Second Smearing With NTP.pdf]], [TIME[2016-11-18T07:59:35.000Z]], [TIME[2020-11-17T01:14:54.790Z]] <https://www.meinbergglobal.com/download/burnicki/Leap%20Second%20Smearing%20With%20NTP.pdf>

[16] [CITE@en[GitHub - google/unsmear: Converts to and from timescales with smeared leap seconds]], [TIME[2020-11-17T01:15:28.000Z]] <https://github.com/google/unsmear>

[17] [CITE@en-US[Look Before You Leap – The Coming Leap Second and AWS (Updated) | AWS News Blog]], [TIME[2020-11-16T23:03:55.000Z]], [TIME[2020-11-17T01:17:19.875Z]] <https://aws.amazon.com/jp/blogs/aws/look-before-you-leap-the-coming-leap-second-and-aws/>

[18] [CITE[Leap-smeared representation of time for high-accuracy applications - viewcontent.cgi]], [TIME[2020-10-13T17:06:14.000Z]], [TIME[2020-11-17T01:18:29.418Z]] <https://www.tdcommons.org/cgi/viewcontent.cgi?article=1388&context=dpubs_series>

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