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Most of you will have seen the announcement on meta.SE that's been out for a while now: We're in the process of switching all sites across the network over to CommonMark. You can find all the nasty details over in the thread on meta.stackexchange so I won't repeat myself here. Since Stack Overflow is by far our largest site and this specific migration is the most challenging one for us, I wanted to take some time to do a tailored announcement here.

We're going to migrate Stack Overflow on Saturday, June 20th 2020.

My estimate is that the migration will take around 20 hours to run.

Will there be any downtime?

There's not gonna be any downtime while we're running the migration. Everything is going to be up as usual. The site will not be placed in read-only mode.

Load on our servers might be a bit higher due to the number crunching going on, but that's about it.

Do we expect any major issues?

No. At this point, we've run this migration for 178 other sites across the network (main + meta sites that is). We learned that we had to tweak a few things along the way (thanks to our users on meta.se for catching and reporting!) but overall I dare to say that the migrations went without major headache. While Stack Overflow is significantly larger and a bigger challenge for our infrastructure, we expect the migration to run without a big impact on the site.

This is not to say that there won't be any issues at all. We're humans dealing with a complex system and there might be some things we didn't think about. I'm going to babysit the migration and will periodically take a look at the numbers, the process and the feedback in this thread. If anything strange comes up, please feel free to chime in.

Why are we running Stack Overflow last, and on a Saturday on top of that?

The migration will likely run for more than 20 hours. While the migration is running there can't be any deployments to production as this would kill the migration job. Initially we planned to run the migration on Stack Overflow as soon as possible but finding a suitable point in time that was not interfering with our day to day business of getting new features and bugfixes out or keeping our infrastructure healthy was more tricky than I anticipated. Now we've found a date and it happens to be after all other sites have been migrated.

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    If something bad happens and Stack Overflow is down, how do you fix stuff without being able to search in Stack Overflow?
    – Pac0
    Commented Jun 19, 2020 at 9:50
  • 23
    @Pac0 select * from answers
    – ivarni
    Commented Jun 19, 2020 at 11:58
  • 6
    @ivarni I was about to say "but it's much more convenient and efficient to use the search box!" But,... no.
    – Pac0
    Commented Jun 19, 2020 at 12:01
  • 6
    @Pac0 Yeah, better do the select, export, send all the data to Google and ask them to index it.
    – ivarni
    Commented Jun 19, 2020 at 12:03
  • Will thecontent be migrated oldest first, newest first, post ID (smallest first, or largest first) or in some order only the database would understand?
    – 1201ProgramAlarm
    Commented Jun 19, 2020 at 15:35
  • 1
    Are you going to fix meta.stackexchange.com/q/349456/566903 (typo in the migration script's edit summary) first?
    – pppery
    Commented Jun 19, 2020 at 18:45
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    why are we migrating
    – user13564783
    Commented Jun 19, 2020 at 19:41
  • @1201ProgramAlarm looks like newest first?
    – Glorfindel
    Commented Jun 19, 2020 at 21:20
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    @DiamondDemon Rationale for migration and other background information is given in the post on the global Meta, which is linked from within this question.
    – Cody Gray - on strike Mod
    Commented Jun 20, 2020 at 2:44
  • Can you enlighten us about the technical tools used to build & maintain this great website? As many of us interact with S.O. on daily basis for technical assistance, so I'm sure many are curious about the technologies used on the front-end and the back-end of this website.
    – Usama Abdulrehman
    Commented Jun 20, 2020 at 13:07
  • Do we get a notification if one of our posts gets edited by this process?
    – Dharman Mod
    Commented Jun 20, 2020 at 16:54
  • @UsamaAbdulrehman see meta.stackexchange.com/questions/10369/….
    – Marijn
    Commented Jun 20, 2020 at 18:34
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    @Dharman no, but you can find in SEDE if your post is touched: data.stackexchange.com/stackoverflow/query/…
    – rene
    Commented Jun 21, 2020 at 13:52
  • Possibly related [bug]: meta.stackoverflow.com/questions/398542/…
    – Kaiido
    Commented Jun 23, 2020 at 3:07
  • 1
    @JW0914 if we're talking about the fact that the syntax highlighting is off (which I agree, it is) we're not talking about the CommonMark implementation or the Markdown renderer but prettify, the syntax highlighter we're using. This is a bug that should be fixed in the library itself, unfortunately it's currently unmaintained. We're working on several bigger improvements here and might be able to cover this issue in a larger round of tweaks.
    – Ham Vocke StaffMod
    Commented Aug 1, 2020 at 14:20

2 Answers 2

Reset to default
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Tab characters in code blocks are replaced by four spaces.

Tab characters in Stack-Snippets are replaced by an inconsistent number of spaces.

This can break any code expecting this character:

const tsv = `This   is  TSV`;
const csv = tsv.replace( /\t/, ',' );

console.log( csv ); // should output "This,is,TSV"

Probably affecting this one too.

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    Tabs have always been replaced with the appropriate amount of spaces in code blocks. This didn't change as part switching to CommonMark.
    – Ham Vocke StaffMod
    Commented Jun 21, 2020 at 8:03
  • @HamVocke probably not an issue in code block but what about snippet?
    – Temani Afif
    Commented Jun 21, 2020 at 8:08
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    @TemaniAfif I'm going to investigate the snippets bug separately. Can repro but need some time to figure out what is going on there.
    – Ham Vocke StaffMod
    Commented Jun 21, 2020 at 8:09
  • @HamVocke to be clear, when you say "the snippets bug", are you talking about the Temani's bug, or about the fact tabs in StackSnippets shouldn't get replaced to spaces? Note that I did edit this answer to split the StackSnippet's case away because it seems that previously it didn't convert tabs in snippets: meta.stackoverflow.com/q/380716 in there the snippet (at bottom of the question) does contain a tab character when rendered normally (in edit mode it is being replaced to 4 spaces).
    – Kaiido
    Commented Jun 22, 2020 at 4:33
1

Possible :

My answer to this question, how to hide <div> in html page in asp.net, gets mangled if I don’t include an XML comment (or possibly a bunch of blank lines or other text).

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    This might explain what happened. CommonMark interprets your code sample as inline HTML code due to a lack of indentation. In your example, you need 4 spaces to make the code sample a continuation of the list item and then you need another 4 spaces to create an indented code block. Using fenced code blocks would work, too.
    – Ham Vocke StaffMod
    Commented Jun 20, 2020 at 21:32

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