5 ms·

I’ve not looked for a long time but the last time I edited it, it was close to realtime* *in the web sense - don’t want to offend any of the real real-time peo

by aidos 6y ago

I’ve not looked for a long time but the last time I edited it, it was close to realtime* *in the web sense - don’t want to offend any of the real real-time people :-)

jedberg 6y ago
Sure, but if the dynamic stuff was down, you just wouldn't be able to edit, but the static part would keep humming right along and never get counted as an outage.
- M2Ys4U 6y ago
  There is some non-edit dynamic stuff too; some templates are written in lua These templates can pull information in from outside of the specific Wikipedia instance, like retrieving properties from Wikidata. Edit: I guess I was wrong, seems like lua modules are only evaluated when there's a change to a page incorporating them: >The programs are run only when the page is "parsed" (when it or a page it incorporates is changed or previewed), not every time you view the output. https://en.wikipedia.org/wiki/Help:Lua_for_beginners#Input https://en.wikipedia.org/wiki/Help:Lua_for_beginners#Input
  - bawolff 6y ago
    You were kind of right - page gets reparsed (and frontend cdn cache cleared, along with a backend cache cleared) anytime someone edits a wikidata entry the lua script uses.
  - Thorrez 6y ago
    Those lua templates seem to be constantly having problems. https://en.wiktionary.org/wiki/a https://en.wiktionary.org/wiki/a >Lua error: not enough memory appears on the page 250 times.
- bawolff 6y ago
  > Sure, but if the dynamic stuff was down, you just wouldn't be able to edit, but the static part would keep humming right along and never get counted as an outage. Frontend cache gets skipped if you have a session cookie (logged in or have been logged in recently or made an edit logged out). So if you edit something, subsequent views are not hitting the static site, so you would notice if it was down
  - jedberg 6y ago
    Yeah, that's how reddit works too, but there are multiple layers of caching behind the CDN that would still hide certain types of outages.
    - bawolff 6y ago
      Wikipedia has a second layer of cache after that of the article html without user interface which is stored in memcache & db (in mediawiki speak this is referred to as the "parser cache"). However typically if the site is down,that layer would go down too, so only the varnish servers really have the potential to hide outages.
z3t4 6y ago
You can also think reads vs writes. Like when there are many reads but few writes it makes sense to have replicas, but if there are many writes and little reads you are better off with "sharding". You can also think RAID, where you have mirrors vs stripes. Often though the two concepts are combined, like in RAID 0+1 or RAID 1+0. Scaling many reads are much more simple then scaling both read/writes though. The holy grail of computing/databases is to build a database that can scale both reads and writes while having decent performance and latency.

by aidos 6y ago

I’ve not looked for a long time but the last time I edited it, it was close to realtime* *in the web sense - don’t want to offend any of the real real-time people :-)

jedberg 6y ago

Sure, but if the dynamic stuff was down, you just wouldn't be able to edit, but the static part would keep humming right along and never get counted as an outage.

M2Ys4U 6y ago
There is some non-edit dynamic stuff too; some templates are written in lua These templates can pull information in from outside of the specific Wikipedia instance, like retrieving properties from Wikidata. Edit: I guess I was wrong, seems like lua modules are only evaluated when there's a change to a page incorporating them: >The programs are run only when the page is "parsed" (when it or a page it incorporates is changed or previewed), not every time you view the output. https://en.wikipedia.org/wiki/Help:Lua_for_beginners#Input https://en.wikipedia.org/wiki/Help:Lua_for_beginners#Input
- bawolff 6y ago
  You were kind of right - page gets reparsed (and frontend cdn cache cleared, along with a backend cache cleared) anytime someone edits a wikidata entry the lua script uses.
- Thorrez 6y ago
  Those lua templates seem to be constantly having problems. https://en.wiktionary.org/wiki/a https://en.wiktionary.org/wiki/a >Lua error: not enough memory appears on the page 250 times.
bawolff 6y ago
> Sure, but if the dynamic stuff was down, you just wouldn't be able to edit, but the static part would keep humming right along and never get counted as an outage. Frontend cache gets skipped if you have a session cookie (logged in or have been logged in recently or made an edit logged out). So if you edit something, subsequent views are not hitting the static site, so you would notice if it was down
- jedberg 6y ago
  Yeah, that's how reddit works too, but there are multiple layers of caching behind the CDN that would still hide certain types of outages.
  - bawolff 6y ago
    Wikipedia has a second layer of cache after that of the article html without user interface which is stored in memcache & db (in mediawiki speak this is referred to as the "parser cache"). However typically if the site is down,that layer would go down too, so only the varnish servers really have the potential to hide outages.

z3t4 6y ago

You can also think reads vs writes. Like when there are many reads but few writes it makes sense to have replicas, but if there are many writes and little reads you are better off with "sharding". You can also think RAID, where you have mirrors vs stripes. Often though the two concepts are combined, like in RAID 0+1 or RAID 1+0. Scaling many reads are much more simple then scaling both read/writes though. The holy grail of computing/databases is to build a database that can scale both reads and writes while having decent performance and latency.