Data synchronization

2020-11-12T12:53:49Z

6041005: some minor edits for British English style

{{FIXME|reason=Work in progress}}

== Origin of data ==
[[Project-GC]]'s statistics are based on data from [[Geocaching.com]]. The data is fetched via the [[Geocaching LIVE api]]. [[Project-GC]] uses a combination of the official API available to general [[Geocaching Partners]] and a private ''Enterprise API''.

The data is still owned by [[Geocaching HQ]] and [[Project-GC]] pays royalties to be allowed to fetch and use the data like it does.

== Fetching of data ==
Geocaching data is continuously being updated in [[Project-GC]]'s databases via the mentioned API. This is done using several parallel methods:
* Continuously fetching newly published [[Geocache]]s. Normal latency 0-35 seconds.
* Continuously updating finds for [[Geocacher]]s. See [[Data synchronization#Refreshing_profiles|Refreshing profiles]] for more details.
* Regular updates of [[Geocache]] information. See [[Data synchronization#Refreshing geocache data|Refreshing geocache data]] for more details.

== Refreshing profiles ==
Geocaching profiles are continuously being updated based on a rule set in the background.

When refreshing Geocaching profiles all new and updated logs are fetched from the API, and also metadata around the Geocaching profile itself, like for example the name of the [[Geocacher]].
=== Rules ===
* [[Geocacher]]s that haven't been refreshed in 24 hours and are [[Paid membership|paying members]] are being refreshed.
* [[Geocacher]]s that haven't been refreshed in 2 days but used [[Project-GC]]'s website the last week are being refreshed.
* [[Geocacher]]s that haven't been refreshed in 7 days but used [[Project-GC]]'s website the last 3 months are being refreshed.
* [[Geocacher]]s whose [[Profile stats]] page has been viewed recently.
* ... and so on, there are ~10 rules like this in place.

Also whenever a user visits the website of [[Project-GC]]s the system checks when that user was last updated. If it's a paying member there will be yet another update if the data is more than 1 hour old. However, this is a job that gets queued in the background and it might take a few minutes until it kicks in.

A [[Geocache]] with new logs will also get scheduled to have its metadata (difficulty, terrain, size, country ...) updated.

It can be noted that a [[Geocacher]] who is a [[Paid membership|paying member]] is more likely to have up-to-date data at [[Project-GC]] when coming back to the site, while freemium users might notice that their data isn't as fresh.

== Refreshing geocache data ==
The refreshing of Geocaching profiles mentioned above makes sure that [[Project-GC]]'s users have frequently updated data, but some [[Geocache]]s might be left out because they have only been logged by [[Geocacher]]s not very active with [[Project-GC]]. Therefore [[Project-GC]] also refreshes [[Geocache]]s.

The frequency of when [[Geocache]]s are refreshed are based on a mix of several variables, like for example:
* Last found
* Hidden date
* Disabled/Archived state
* Number of logs

When a [[Geocache]] gets refreshed metadata about the [[Geocache]] gets updated in the database. Also all new/updated logs are updated in the system.

== Log data ==
The log entries fetched are the same, regardless if they are fetched from Geocaching profiles or from Geocache data. It's just different approaches/angles to retrieve the same information. If Geocaching profile X has found Geocache GCX, then GCX automatically also has a log from Geocaching profile X.

== Databases ==
Now most [[Geocache]] data and logs exists in the primary database cluster and are fairly up-to-date. Most of the data will only be hours old in the database, but a fair share is expected to be 24-36 hours old.

However [[Project-GC]] has more than one database cluster. Most statistics on the web are created based on data from another database cluster. The primary database cluster replicates its data every 4 hours o the second cluster, adding an additional ~4 hours of latency. As an example most top lists are based on this secondary cluster, while [[Profile stats]] are not.

As a technical note, the primary database cluster is a row-based relational database. The secondary cluster is created and meant for database harvesting and is a column-oriented DBMS.

== Statistics ==
As mentioned in [[Data synchronization#Databases|Databases]], most statistics are based on a secondary database cluster. Even if [[Project-GC]] itself has up-to-date profile data the secondary database cluster might still have the old data. This is due to the fact that a full replica of the data-set is copied every four hours.

Most top lists are using this secondary cluster. Basically everything that gets heavily computed (data harvesting) uses the secondary cluster, while more raw fetches use the primary one. [[Profile stats]] is an exception.

It's also worth mentioning here as well that [[Lab caches]] generally aren't included in statistics. They aren't technically compatible and it would be very complex to do this. Again, [[Profile stats]] can be an exception.

Finally, all generated statistics are [[Data caching|cached]]. The period for which it is cached varies but anything between 5 minutes and 1 hour is very common. So if two people ask for the same statistic, it will only be computed the first time, the second person will receive a cached version. This has the downside that it potentially also adds more latency and shows older data in some cases.

== Profile stats ==
* Generated from ''current state'' at the date written in the header.
* Labs included depending on setting and paying/freemium.
* Cached for 7 days for freemium, 24h for paying.
* Caching is not shared between the user the data is about and other viewers.
* Based on the primary database cluster.

== Challenge checkers ==
Challenge checkers use a mix of the different database clusters. If the [[Checker script]] fetches the user's finds from [[Project-GC]] it will use the primary database cluster. But some other more advanced API methods might use the secondary database cluster instead. This is for performance reasons.

== Special numbers ==
Some statistics are very special since they are based on pre-calculated values. This is usually because it would be extremely hard to calculate this in real-time, therefore it's based on pre-calculated values. [[Project-GC]] calculates the following data for every [[Geocacher]] in the background on a regular basis. Normally daily, but there are some exceptions to it (usually that some users gets calculated more often).
* D/T loops
* streaks
* calendar loops

This does not affect [[Profile stats]]. If numbers like these are needed, [[Profile stats]] calculates them itself instead of using pre-calculated data. This is also needed since it may have [[Labcache]] data merged.

Project-GC - User contributions [en]

Data synchronization