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Commits
| Author | SHA1 | Message | Date | |
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  aschmitzandEugen Rochko
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97c02c3389 |
Make IdsToBigints (mostly!) non-blocking (#5088)
* Make IdsToBigints (mostly!) non-blocking This pulls in GitLab's MigrationHelpers, which include code to make column changes in ways that Postgres can do without locking. In general, this involves creating a new column, adding an index and any foreign keys as appropriate, adding a trigger to keep it populated alongside the old column, and then progressively copying data over to the new column, before removing the old column and replacing it with the new one. A few changes to GitLab's MigrationHelpers were necessary: * Some changes were made to remove dependencies on other GitLab code. * We explicitly wait for index creation before forging ahead on column replacements. * We use different temporary column names, to avoid running into index name length limits. * We rename the generated indices back to what they "should" be after replacing columns. * We rename the generated foreign keys to use the new column names when we had to create them. (This allows the migration to be rolled back without incident.) # Big Scary Warning There are two things here that may trip up large instances: 1. The change for tables' "id" columns is not concurrent. In particular, the stream_entries table may be big, and does not concurrently migrate its id column. (On the other hand, x_id type columns are all concurrent.) 2. This migration will take a long time to run, *but it should not lock tables during that time* (with the exception of the "id" columns as described above). That means this should probably be run in `screen` or some other session that can be run for a long time. Notably, the migration will take *longer* than it would without these changes, but the website will still be responsive during that time. These changes were tested on a relatively large statuses table (256k entries), and the service remained responsive during the migration. Migrations both forward and backward were tested. * Rubocop fixes * MigrationHelpers: Support ID columns in some cases This doesn't work in cases where the ID column is referred to as a foreign key by another table. * MigrationHelpers: support foreign keys for ID cols Note that this does not yet support foreign keys on non-primary-key columns, but Mastodon also doesn't yet have any that we've needed to migrate. This means we can perform fully "concurrent" migrations to change ID column types, and the IdsToBigints migration can happen with effectively no downtime. (A few operations require a transaction, such as renaming columns or deleting them, but these transactions should not block for noticeable amounts of time.) The algorithm for generating foreign key names has changed with this, and therefore all of those changed in schema.rb. * Provide status, allow for interruptions The MigrationHelpers now allow restarting the rename of a column if it was interrupted, by removing the old "new column" and re-starting the process. Along with this, they now provide status updates on the changes which are happening, as well as indications about when the changes can be safely interrupted (when there are at least 10 seconds estimated to be left before copying data is complete). The IdsToBigints migration now also sorts the columns it migrates by size, starting with the largest tables. This should provide administrators a worst-case scenario estimate for the length of migrations: each successive change will get faster, giving admins a chance to abort early on if they need to run the migration later. The idea is that this does not force them to try to time interruptions between smaller migrations. * Fix column sorting in IdsToBigints Not a significant change, but it impacts the order of columns in the database and db/schema.rb. * Actually pause before IdsToBigints |
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aschmitzandEugen Rochko
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dd4ef69839 |
Hardcode IdToBigints migration columns (#5039)
This addresses a comment during review: https://github.com/tootsuite/mastodon/pull/4801#discussion_r139337452 This means we'll need to make sure that all _id columns going forward are bigints, but that should happen automatically in most cases. |
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aschmitzandEugen Rochko
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669fe9ee06 |
Change IDs to strings rather than numbers in API JSON output (#5019)
* Fix JavaScript interface with long IDs Somewhat predictably, the JS interface handled IDs as numbers, which in JS are IEEE double-precision floats. This loses some precision when working with numbers as large as those generated by the new ID scheme, so we instead handle them here as strings. This is relatively simple, and doesn't appear to have caused any problems, but should definitely be tested more thoroughly than the built-in tests. Several days of use appear to support this working properly. BREAKING CHANGE: The major(!) change here is that IDs are now returned as strings by the REST endpoints, rather than as integers. In practice, relatively few changes were required to make the existing JS UI work with this change, but it will likely hit API clients pretty hard: it's an entirely different type to consume. (The one API client I tested, Tusky, handles this with no problems, however.) Twitter ran into this issue when introducing Snowflake IDs, and decided to instead introduce an `id_str` field in JSON responses. I have opted to *not* do that, and instead force all IDs to 64-bit integers represented by strings in one go. (I believe Twitter exacerbated their problem by rolling out the changes three times: once for statuses, once for DMs, and once for user IDs, as well as by leaving an integer ID value in JSON. As they said, "If you’re using the `id` field with JSON in a Javascript-related language, there is a very high likelihood that the integers will be silently munged by Javascript interpreters. In most cases, this will result in behavior such as being unable to load or delete a specific direct message, because the ID you're sending to the API is different than the actual identifier associated with the message." [1]) However, given that this is a significant change for API users, alternatives or a transition time may be appropriate. 1: https://blog.twitter.com/developer/en_us/a/2011/direct-messages-going-snowflake-on-sep-30-2011.html * Additional fixes for stringified IDs in JSON These should be the last two. These were identified using eslint to try to identify any plain casts to JavaScript numbers. (Some such casts are legitimate, but these were not.) Adding the following to .eslintrc.yml will identify casts to numbers: ~~~ no-restricted-syntax: - warn - selector: UnaryExpression[operator='+'] > :not(Literal) message: Avoid the use of unary + - selector: CallExpression[callee.name='Number'] message: Casting with Number() may coerce string IDs to numbers ~~~ The remaining three casts appear legitimate: two casts to array indices, one in a server to turn an environment variable into a number. * Back out RelationshipsController Change This was made to make a test a bit less flakey, but has nothing to do with this branch. * Change internal streaming payloads to stringified IDs as well Per https://github.com/tootsuite/mastodon/pull/5019#issuecomment-330736452 we need these changes to send deleted status IDs as strings, not integers. |