Sundial

Accurate and scalable than the previously used service, ntpd, which made it an easy decision for us to replace ntpd in our infrastructure. Chrony was just one component of a multi-layered precision time synchronization service, backed by atomic clocks and GPS systems on satellites. Below is the architecture diagram of the four-layered service.With this service, they were able to improve time precision from tens of milliseconds to hundreds of microseconds.Sundial (Apr 2020)There was a paper that recently appeared in OSDI 2020 called Sundial: Fault-tolerant Clock Synchronization for Datacenters. The authors present a fault-tolerant clock synchronization system for datacenters that achieves around 100ns (yes, that’s nanoseconds) time-uncertainty bound under various types of failures. From the abstract: Sundial provides fast failure detection based on frequent synchronization messages in hardware. Sundial enables fast failure recovery using a novel graph based algorithm to precompute a backup plan that is generic to failures. Through experiments in a >500-machine testbed and large-scale simulations, we show that Sundial can achieve ~100ns time-uncertainty bound under different types of failures, which is more than two orders of magnitude lower than the state-of-the-art solutions. Sundial is able to get epsilon less than 100 nanoseconds using the following techniques to achieve better time synchronization:Performs timestamping and synchronization at L2 data link level in a point-to-point manner using the hardware NIC. Doing synchronization at the hardware level enables frequent synchronization to compensate for the uncontrollable clock drifts of quartz clocks. They send a synchronization signal every 500 microseconds to reduce clock drift of quartz clocks and to keep epsilon very small. Performing synchronization this frequently would not work over software.Sundial uses a spanning tree as the multi-hop synchronization structure and synchronizes the nodes with respect to a single root. Sundial uses predetermined backup parents to default to, so it can recover fast from link and root failures.ConclusionWe discussed a few different approaches for distributed time synchronization in this post, as summarized in the below table.We picked HLC, which combines the best of logical clocks and physical clocks. This ensured that we were able to meet the fundamental design principles for YugabyteDB mentioned earlier.When we began the YugabyteDB project in 2016, our premise was that clock synchronization in public clouds would keep getting better over time. This premise has already proven to be true with services such as Amazon Time Sync Service, which launched in 2017 followed by Time Sync for Azure.Lastly, it

Maglaon, idinagdag ang mga marker sa paligid ng base ng monumento upang ipahiwatig ang karagdagang mga subdibisyon ng oras. Iba pang mga Sun Clock Ang isa pang Egyptian shadow clock o sundial ay ginamit noong mga 1500 BCE upang sukatin ang pagdaan ng "mga oras." Hinati ng device na ito sa 10 bahagi ang isang araw na nasisikatan ng araw, kasama ang dalawang "oras ng takip-silim" sa umaga at gabi. Kapag ang mahabang tangkay na may limang variably spaced mark ay nakatuon sa silangan at kanluran sa umaga, ang isang nakataas na crossbar sa silangang dulo ay naglagay ng gumagalaw na anino sa mga marka. Sa tanghali, inikot ang device sa kabilang direksyon upang sukatin ang "mga oras" ng hapon.Ang merkhet, ang pinakalumang kilalang astronomical tool, ay isang pag-unlad ng Egypt noong 600 BCE. Dalawang merkhets ang ginamit upang magtatag ng hilaga-timog na linya sa pamamagitan ng paghanay sa kanila sa Pole Star. Magagamit ang mga ito upang markahan ang mga oras ng gabi sa pamamagitan ng pagtukoy kung kailan tumawid ang ilang mga bituin sa meridian.Sa paghahanap ng higit pang katumpakan sa buong taon, ang mga sundial ay nagbago mula sa mga patag na pahalang o patayong mga plato patungo sa mga anyo na mas detalyado. Ang isang bersyon ay ang hemispherical dial, isang hugis-mangkok na depresyon na pinutol sa isang bloke ng bato na may gitnang patayong gnomon o pointer at may nakasulat na mga hanay ng mga linya ng oras. Ang hemicycle, na sinasabing naimbento noong mga 300 BCE, ay inalis ang walang silbi na kalahati ng hemisphere upang magbigay ng hitsura ng kalahating mangkok na hiwa sa gilid ng isang parisukat na bloke. Pagsapit ng 30 BCE, maaaring ilarawan ng Romanong arkitekto na si Marcus Vitruvius ang 13 iba't ibang istilo ng sundial na ginagamit sa

Think of it as your “Electronic Toolbox”. The iGadget App for iPhone and Apple Watch features a variety of useful and entertaining gadgets, each with a delightfully “retro” analog appearance.Currently, the iGadget App supports the following Gadgets:• Altimeter• Barometer• Compass*• Hygrometer• Magnifying Glass*• Metronome*• Rain Gauge*• Ruler*• Speedometer• Spirit Level*• Sundial• Telescope*• Thermometer• Vertical Speed Indicator• VU Meter• Weather Vane* Indicates Gadgets supported by iPhone only.Altimeter - The Altimeter Gadget displays your altitude as either a standard aviation Altimeter, or as a ‘digital’ gauge, both of which are calibrated in either meters or feet.Barometer - Displays the atmospheric pressure at your current location, with readout in hPa, mmHg and inHg.Compass - We all want to know where we’re going, don’t we? Now your iPhone can show you at a glance your current compass heading. Just like a ship’s compass, the entire dial of the Compass Gadget rotates, so the North arrow always points to magnetic North. Hygrometer - Displays the humidity level (%) at your current location.Magnifying Glass - Use the iPhone's camera to view small objects and text at 10x magnification.Metronome - Select a frequency between "Grave" (42 beats per minute) and "Prestissimo" (208 beats per minute).Rain Gauge - View the cumulative rainfall in your current location for the last hour, last day or last week.Ruler - Have you ever needed to measure something, but couldn’t lay your hands on a ruler? Just use your iPhone! This Gadget displays a ruler, precisely calibrated to the size of your iPhone’s screen. Yet another reason to love the larger screen-size of your iPhone 6/6s/7 Plus!Speedometer - View your current speed using one of several classic automobile or motorcycle speedometers.Spirit Level - Use your iPhone as a (relatively inaccurate!) Spirit Level, to measure the level of your desk, for example.Sundial - An electronic sundial which automatically rotates the Sundial’s face so that it is orientated to the equator, whether you are in the Northern or Southern hemisphere. During daylight hours, the Sundial Gadget displays the shadow cast by the electronic ‘gnomon’ (that’s the name for the pointy thing on a Sundial). So you can use the sun’s shadow to read the time of day at your current location, even if it’s cloudy/raining. Just don’t expect it to tell you the time after sunset!Telescope - Displays the camera image magnified 2x, 5x or 10x.Thermometer - Displays the ambient temperature for your current location, based on local weather reports. Calibrated in degrees Centigrade and Fahrenheit.Vertical Speed Indicator - Displays your vertical speed, as per a standard aviation VSI gauge. Calibrated in thousands of feet per minute or thousands of meters per minute.VU Meter - Displays the ambient noise level, as detected by the microphone of your iPhone or Apple Watch.Weather Vane - Displays the wind speed and direction at your current location. The vane's needle points into the wind, while the wind's strength is indicated by the speed at which the anemometer spins. ConfigurabilityOn the iPhone, use the Gadget Gallery to select a specific