Month: November 2016

Server update, 2016-11-21

This is our first release since the NewHost move, so it’s a mishmash of changes required for that and whatever else people submitted in between.

First, some dependency changes: memcached has been dropped as a dependency. We now use Redis as a cache, which had already been used for storing login sessions. In production we run two separate Redis instances: one as a cache (note: configure the DBDefs settings CACHE_MANAGER_OPTIONS and PLUGIN_CACHE_OPTIONS) and one as a persistent session store (DATASTORE_REDIS_ARGS). But it’s also safe (if less flexible) to use a single Redis instance without a maxmemory setting for both, because cached entries will expire by default. So if you already had Redis running locally, you may not need to make any changes to your configuration.

This release also requires the Perl module DBD::Pg to be version 3, which you may already have. If not, you can upgrade only that module with this command:

cpanm TURNSTEP/DBD-Pg-3.5.3.tar.gz

Thanks also to chirlu for upgrading reCAPTCHA on our registration page (which has hopefully reduced new spam accounts), Zastai for fixing some oversights in our JSON webservice, and reosarevok for removing the restriction on score URLs.

The git tag is v-2016-11-21.

Bug

  • [MBS-8762] – ISNI doesn’t appear on JSON WS
  • [MBS-9035] – Coro dependency causes build failure on Perl 5.22 and newer
  • [MBS-9091] – JSON WS: Aliases do not include begin/end date and ended flag
  • [MBS-9127] – NewHost: UI language does not match “lang” in cookie
  • [MBS-9132] – cannot add an alias (area)

Improvement

  • [MBS-9031] – Replace all usages of memcached with redis
  • [MBS-9130] – Upgrade to new reCAPTCHA (version 2)

Task

  • [MBS-9096] – Upgrade DBD::Pg to version 3
  • [MBS-9110] – Disable the score whitelist

The end of the replication nightmare!

I’m pleased to report that our nightmare of finding/reconstructing the missing replication packets is finally over!

Through many heroic hours of work, Bitmap and Chirlu have reconstructed the missing replication packets. All clients should now be on their way to being up to date. We’ve learned a number of lessons (some good, some bad — that’s life, right?) in this ordeal and we hope to avoid these issues in the future.

An integral part of this recovery process were a number of people from our community who helped us: Users mbcz, rembo10 and xeam sent us their complete DB dumps! Bitmap used these to sanity check and diff several other database to finally extract the missing packets. Thank you for dropping what you were doing and sending us a few GB of data over blazingly fast connections. Without you this would not have been possible; and this is not an exaggeration. Thank you!

After some more rest we’re going to continue to put out smaller fires that remain from the move to NewHost, but for now, the big fires are put out. Just in time for the weekend!

In the 11 year history of the replication stream we’ve had to have users restart their stream about 3-4 times because of problems on our end. Zero would’ve been nicer, but I’m proud that we’ve been able to make this system work for so long. On a daily basis we seem to have about 400 replicated copies of MusicBrainz running all over the world. Clearly this part of our service is well used and I sleep a little better at night knowing that our most critical data is backed up across the globe.

Just for fun, here is a graph of the replication API usage over the last 6 months:

hourly-api-usage.png

Towards the end the graph shows the week plus long break, then a small blip as some of our replicas got unstuck yesterday and the much larger spike shows the rest of the replicas getting unstuck. Now, as to what caused the blip in mid-October — I have no idea.

Anyways, please accept my apologies for the replication stream outage and keep replicating!

Thanks!

Replication update: Do you have a DB that could help us?

In my post from yesterday I talked about our continuing struggle to fix our replication stream. Overnight we learned two new things:

  1. The lengthy hard drive recovery process has failed and yielded no useful results. 😦
  2. We have a working DB diff program in place that allows us to create missing replication packets from two DBs at known packet numbers.

#2 is a great step forward in fixing our replication stream, but we’re missing a specific replicated database at a specific point in time. If you have a replicated database, please read on and see if you can help us:

  1. Is your database at replication packet 99847? The way to find out your current replication sequence is to look in slave.log in your server directory or to issue the query 
    select current_replication_sequence from replication_control;

    at the SQL prompt.

  2. Do you have a complete replicated MusicBrainz database, including the cover_art_archive schema?
  3. Are you willing to make a dump of the DB and send it to us?
  4. Do you have a fast internet connection to make #3 possible?

If you’ve answered yes to all of the above, please send email to support at metabrainz dot org.

Thanks!

 

Move to NewHost and Replication Update

It has been a long week since our move to the new hosting provider in Germany. Our move across the Atlantic worked out fairly well in the grand scheme of things. The new servers are performing well, the site is more stable and we have a modern infrastructure for most of our projects.

However, such moves are not without problems. While we didn’t encounter many problems, the most significant one we did encounter was the failure to copy two small replication packets off the old servers. We didn’t notice this problem until after the server in question had been decommissioned. Ooops.

And thus began a recovery effort that is almost worthy of a bad Hollywood B-movie plot. Between myself traveling and the team finishing the most critical migration bits, it took 2 days for us to realize the problem and find a volunteer to fetch the drives from the broken server. Only in a small and wealthy place such as San Luis Obispo, could a stack of recycled servers sit in an open container for 2 days and not be touched at all. My friend collected the drives and immediately noticed that the drives were damaged in the recycling process, which isn’t surprising. And we can consider ourselves really lucky that this drive didn’t contain private data — those drives have been physically destroyed!

Since then, my friend has been working with Linux disk recovery tools to try and recover the two replication packets off the drive. Given that he is working with a 1TB drive, this recovery process takes a while and must be fully completed before attempting to pull data off the drive. For now we wait.

At the same time, we’re actively cobbling together a method to regenerate the lost packets. In theory it is possible, but it involves heroic efforts of stupidity. And we’re expending that effort, but so far, it bears no fruit.

In the meantime, for all of the people who use our replicated (Live Data) feed — you have the following choices:

  1. If you need data updates flowing again as soon as possible, we strongly recommend importing a new data set. We have a new data dump and fresh replication packets being put out, so you can do this at any time you’re ready.
  2. If the need for updates is not urgent yet and you’d rather not reload the data, sit tight. We’re continuing our stupidly heroic efforts to recover the replication packets.
  3. Chocolate: It really makes everything better. It may not help with your data problems, but at least it takes the edge off.

We’re terribly sorry for the hassle in all of this! Our geek pride has been sufficiently dinged that our chocolate coping mechanisms will surely cause us to put on a pound or two.

Stay tuned!

UPDATE 1: The first recovery examination has not located the files, but my friend will do a second pass tomorrow and turn over file fragments to us that might allow us to recover files. But that won’t be for another 8 hours or so.

Final sprint towards NewHost

So tomorrow is the day when the old servers at Digital West will be put to rest. Our developers and system administrator have been hard at work over the last few weeks (and especially the last few days!) getting everything ready for a hopefully smooth transition to hosting everything at Hetzner in Germany.

The vast majority of our sites and services are in fact already being served from Germany, but the largest one—musicbrainz.org—remains in the US for another night.

Our transition of the final services, such as musicbrainz.org, has already started, but the very last sprint of moving the remaining bits over will start tomorrow, November 8th, at around 6 AM EST / noon UTC / 13:00 CET and will follow the plan laid out in this Google document:
https://docs.google.com/document/d/1MgqZ4hiKC0MZJ400ZCOD8JlcjBjh4GNpakauf51YKQQ/edit?usp=sharing

Expect some downtime, plenty of read-only time, and general wonkiness as we get the last gears set in place to hopefully keep us running smoothly for the next several years to come!