crash-consistent layer map through index_part.json #5198

koivunej · 2023-09-05T07:45:48Z

Fixes #5172 as it:

removes recoinciliation with remote index_part.json and accepts remote index_part.json as the truth, deleting any local progress which is yet to be reflected in remote
moves to prefer remote metadata

Additionally:

tests with single LOCAL_FS parametrization are cleaned up
adds a test case for branched (non-bootstrap) local only timeline availability after restart

github-actions · 2023-09-05T08:00:47Z

2298 tests run: 2182 passed, 0 failed, 116 skipped (full report)

Code coverage (full report)

functions: 52.9% (8263 of 15614 functions)
lines: 80.5% (48166 of 59830 lines)

_{The comment gets automatically updated with the latest test results
2307cf1 at 2023-10-17T08:59:59.618Z :recycle:}

pageserver/src/tenant/remote_timeline_client.rs

test_runner/fixtures/neon_fixtures.py

test_runner/fixtures/remote_storage.py

pageserver/src/tenant/timeline/init.rs

Remote storage cleanup split from #5198: - pageserver, extensions, and safekeepers now have their separate remote storage - RemoteStorageKind has the configuration code - S3Storage has the cleanup code - with MOCK_S3, pageserver, extensions, safekeepers use different buckets - with LOCAL_FS, `repo_dir / "local_fs_remote_storage" / $user` is used as path, where $user is `pageserver`, `safekeeper` - no more `NeonEnvBuilder.enable_xxx_remote_storage` but one `enable_{pageserver,extensions,safekeeper}_remote_storage` Should not have any real changes. These will allow us to default to `LOCAL_FS` for pageserver on the next PR, remove `RemoteStorageKind.NOOP`, work towards #5172. Co-authored-by: Alexander Bayandin <alexander@neon.tech>

Assorted flakyness fixes from #5198, might not be flaky on `main`. Migrate some tests using neon_simple_env to just neon_env_builder and using initial_tenant to make flakyness understanding easier. (Did not understand the flakyness of `test_timeline_create_break_after_uninit_mark`.) `test_download_remote_layers_api` is flaky because we have no atomic "wait for WAL, checkpoint, wait for upload and do not receive any more WAL". `test_tenant_size` fixes are just boilerplate which should had always existed; we should wait for the tenant to be active. similarly for `test_timeline_delete`. `test_timeline_size_post_checkpoint` fails often for me with reading zero from metrics. Give it a few attempts.

test_runner/regress/test_branching.py

#5198 (comment)

pageserver/src/tenant.rs

g#

test_runner/regress/test_branching.py

jcsp · 2023-10-16T08:57:31Z

Pushed a commit to update the test docstrings.

jcsp · 2023-10-16T17:07:17Z

The build failure was from a review comment suggested change, fixed it.

jcsp · 2023-10-17T08:19:53Z

Merged main to resolve a conflict.

- finally add an `#[instrument]` to Timeline::create_image_layers, making it easier to see that something is happening because we create image layers - format some macro context code - add a warning not to create new validation functions a la parse do not validate Split off from #5198.

The `writer.finish()` methods already fsync the inode, using `VirtualFile::sync_all()`. All that the callers need to do is fsync their directory, i.e., the timeline directory. Note that there's a call in the new compaction code that is apparently dead-at-runtime, so, I couldn't fix up any fsyncs there [Link](https://github.com/neondatabase/neon/blob/502b69b33bbd4ad1b0647e921a9c665249a2cd62/pageserver/src/tenant/timeline/compaction.rs#L204-L211). In the grand scheme of things, layer durability probably doesn't matter anymore because the remote storage is authoritative at all times as of #5198. But, let's not break the discipline in htis commit. part of #6663

The `writer.finish()` methods already fsync the inode, using `VirtualFile::sync_all()`. All that the callers need to do is fsync their directory, i.e., the timeline directory. Note that there's a call in the new compaction code that is apparently dead-at-runtime, so, I couldn't fix up any fsyncs there [Link](https://github.com/neondatabase/neon/blob/502b69b33bbd4ad1b0647e921a9c665249a2cd62/pageserver/src/tenant/timeline/compaction.rs#L204-L211). Note that layer durability still matters somewhat, even after #5198 which made remote storage authoritative. We do have the layer file length as an indicator, but no checksums on the layer file contents. So, a series of overwrites without fsyncs in the middle, plus a subsequent crash, could cause us to end up in a state where the file length matches but the contents are garbage. part of #6663

fixes #7790 (duplicating most of the issue description here for posterity) # Background From the time before always-authoritative `index_part.json`, we had to handle duplicate layers. See the RFC for an illustration of how duplicate layers could happen: https://github.com/neondatabase/neon/blob/a8e6d259cb49d1bf156dfc2215b92c04d1e8a08f/docs/rfcs/027-crash-consistent-layer-map-through-index-part.md?plain=1#L41-L50 As of #5198 , we should not be exposed to that problem anymore. # Problem 1 We still have 1. [code in Pageserver](https://github.com/neondatabase/neon/blob/82960b2175211c0f666b91b5258c5e2253a245c7/pageserver/src/tenant/timeline.rs#L4502-L4521) than handles duplicate layers 2. [tests in the test suite](https://github.com/neondatabase/neon/blob/d9dcbffac37ccd3331ec9adcd12fd20ce0ea31aa/test_runner/regress/test_duplicate_layers.py#L15) that demonstrates the problem using a failpoint However, the test in the test suite doesn't use the failpoint to induce a crash that could legitimately happen in production. What is does instead is to return early with an `Ok()`, so that the code in Pageserver that handles duplicate layers (item 1) actually gets exercised. That "return early" would be a bug in the routine if it happened in production. So, the tests in the test suite are tests for their own sake, but don't serve to actually regress-test any production behavior. # Problem 2 Further, if production code _did_ (it nowawdays doesn't!) create a duplicate layer, the code in Pageserver that handles the condition (item 1 above) is too little and too late: * the code handles it by discarding the newer `struct Layer`; that's good. * however, on disk, we have already overwritten the old with the new layer file * the fact that we do it atomically doesn't matter because ... * if the new layer file is not bit-identical, then we have a cache coherency problem * PS PageCache block cache: caches old bit battern * blob_io offsets stored in variables, based on pre-overwrite bit pattern / offsets * => reading based on these offsets from the new file might yield different data than before # Solution - Remove the test suite code pertaining to Problem 1 - Move & rename test suite code that actually tests RFC-27 crash-consistent layer map. - Remove the Pageserver code that handles duplicate layers too late (Problem 1) - Use `RENAME_NOREPLACE` to prevent over-rename the file during `.finish()`, bail with an error if it happens (Problem 2) - This bailing prevents the caller from even trying to insert into the layer map, as they don't even get a `struct Layer` at hand. - Add `abort`s in the place where we have the layer map lock and check for duplicates (Problem 2) - Note again, we can't reach there because we bail from `.finish()` much earlier in the code. - Share the logic to clean up after failed `.finish()` between image layers and delta layers (drive-by cleanup) - This exposed that test `image_layer_rewrite` was overwriting layer files in place. Fix the test. # Future Work This PR adds a new failure scenario that was previously "papered over" by the overwriting of layers: 1. Start a compaction that will produce 3 layers: A, B, C 2. Layer A is `finish()`ed successfully. 3. Layer B fails mid-way at some `put_value()`. 4. Compaction bails out, sleeps 20s. 5. Some disk space gets freed in the meantime. 6. Compaction wakes from sleep, another iteration starts, it attempts to write Layer A again. But the `.finish()` **fails because A already exists on disk**. The failure in step 5 is new with this PR, and it **causes the compaction to get stuck**. Before, it would silently overwrite the file and "successfully" complete the second iteration. The mitigation for this is to `/reset` the tenant.

koivunej changed the title ~~No more noop tests~~ test: No more RemoteStorageKind.NOOP Sep 5, 2023

koivunej force-pushed the no_more_noop_tests branch from e5ae301 to 25ecce6 Compare September 5, 2023 07:52

koivunej force-pushed the no_more_noop_tests branch from 25ecce6 to e9cfebd Compare September 5, 2023 10:46

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koivunej force-pushed the no_more_noop_tests branch 3 times, most recently from 453486c to 689c6d0 Compare September 6, 2023 18:14

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jcsp reviewed Sep 7, 2023

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This was referenced Sep 7, 2023

Misc test flakyness fixes #5233

Merged

test: Remote storage refactorings #5243

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jcsp reviewed Sep 8, 2023

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koivunej mentioned this pull request Sep 8, 2023

Epic: crash-consistent layer map through index_part.json #5172

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koivunej force-pushed the no_more_noop_tests branch from 9d054b2 to 518c278 Compare September 8, 2023 12:17

koivunej mentioned this pull request Sep 8, 2023

fix: LocalFs root in test_compatibility is PosixPath('...') #5261

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koivunej force-pushed the no_more_noop_tests branch from 518c278 to 474bbf3 Compare September 8, 2023 17:36

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koivunej added 4 commits October 12, 2023 18:27

refactor: needless clone

0119f9f

refactor: move uses, add uses

ba118a8

test: rename availability to is_deleted

0625a0f

test: cleanup comments

a88f41b

jcsp approved these changes Oct 13, 2023

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missing format string

1094a26

#5198 (comment)

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use constant for metadata file name

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g#

jcsp reviewed Oct 13, 2023

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Update test docstrings

134b268

Fix compile error from review comment 1094a26

090c089

jcsp enabled auto-merge (squash) October 16, 2023 17:07

Merge remote-tracking branch 'upstream/main' into no_more_noop_tests

2307cf1

jcsp merged commit 9e14493 into main Oct 17, 2023
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jcsp deleted the no_more_noop_tests branch October 17, 2023 09:04

jcsp mentioned this pull request Oct 23, 2023

Attempt to perform query just after pageserver restart fails #5620

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problame mentioned this pull request Oct 24, 2023

pageserver: schedule frozen layer uploads inside the layers lock #5639

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This was referenced Mar 1, 2024

layer file creation: remove redundant fsync()s #6983

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pageserver: sync on startup (eliminate bug class of unclear durability after abort()) #6989

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This was referenced May 17, 2024

re-assess severity of duplicate layers: nowadays it cannot happen & we should panic/abort() early if they do #7790

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fix(pageserver): duplicate layers can cause corruption #7799

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crash-consistent layer map through index_part.json #5198

crash-consistent layer map through index_part.json #5198

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jcsp commented Oct 17, 2023

crash-consistent layer map through index_part.json #5198

crash-consistent layer map through index_part.json #5198

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