It used to be a separate piece of state, but after 9a6c0be823 it's just
an alias for the Tenant being in Attaching state. It was only used in
one assertion in a test, but that check doesn't make sense anymore, so
just remove it.
Fixes https://github.com/neondatabase/neon/issues/2930
I'm not a fan of "Paused", for two reasons:
- Paused implies that the tenant/timeline with no activity on it. That's
not true; the tenant/timeline can still have active tasks working on it.
- Paused implies that it can be resumed later. It can not. A tenant or
timeline in this state cannot be switched back to Active state anymore.
A completely new Tenant or Timeline struct can be constructed for the
same tenant or timeline later, e.g. if you detach and later re-attach
the same tenant, but that's a different thing.
Stopping describes the state better. I also considered "ShuttingDown",
but Stopping is simpler as it's a single word.
The code in this change was extracted from PR #2595, i.e., Heikki’s draft
PR for on-demand download.
High-Level Changes
- storage_sync module rewrite
- Changes to Tenant Loading
- Changes to Timeline States
- Crash-safe & Resumable Tenant Attach
There are several follow-up work items planned.
Refer to the Epic issue on GitHub:
https://github.com/neondatabase/neon/issues/2029
Metadata:
closes https://github.com/neondatabase/neon/pull/2785
unsquashed history of this patch: archive/pr-2785-storage-sync2/pre-squash
Co-authored-by: Dmitry Rodionov <dmitry@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
===============================================================================
storage_sync module rewrite
===========================
The storage_sync code is rewritten. New module name is storage_sync2, mostly to
make a more reasonable git diff.
The updated block comment in storage_sync2.rs describes the changes quite well,
so, we will not reproduce that comment here. TL;DR:
- Global sync queue and RemoteIndex are replaced with per-timeline
`RemoteTimelineClient` structure that contains a queue for UploadOperations
to ensure proper ordering and necessary metadata.
- Before deleting local layer files, wait for ongoing UploadOps to finish
(wait_completion()).
- Download operations are not queued and executed immediately.
Changes to Tenant Loading
=========================
Initial sync part was rewritten as well and represents the other major change
that serves as a foundation for on-demand downloads. Routines for attaching and
loading shifted directly to Tenant struct and now are asynchronous and spawned
into the background.
Since this patch doesn’t introduce on-demand download of layers we fully
synchronize with the remote during pageserver startup. See details in
`Timeline::reconcile_with_remote` and `Timeline::download_missing`.
Changes to Tenant States
========================
The “Active” state has lost its “background_jobs_running: bool” member. That
variable indicated whether the GC & Compaction background loops are spawned or
not. With this patch, they are now always spawned. Unit tests (#[test]) use the
TenantConf::{gc_period,compaction_period} to disable their effect (15db566).
This patch introduces a new tenant state, “Attaching”. A tenant that is being
attached starts in this state and transitions to “Active” once it finishes
download.
The `GET /tenant` endpoints returns `TenantInfo::has_in_progress_downloads`. We
derive the value for that field from the tenant state now, to remain
backwards-compatible with cloud.git. We will remove that field when we switch
to on-demand downloads.
Changes to Timeline States
==========================
The TimelineInfo::awaits_download field is now equivalent to the tenant being
in Attaching state. Previously, download progress was tracked per timeline.
With this change, it’s only tracked per tenant. When on-demand downloads
arrive, the field will be completely obsolete. Deprecation is tracked in
isuse #2930.
Crash-safe & Resumable Tenant Attach
====================================
Previously, the attach operation was not persistent. I.e., when tenant attach
was interrupted by a crash, the pageserver would not continue attaching after
pageserver restart. In fact, the half-finished tenant directory on disk would
simply be skipped by tenant_mgr because it lacked the metadata file (it’s
written last). This patch introduces an “attaching” marker file inside that is
present inside the tenant directory while the tenant is attaching. During
pageserver startup, tenant_mgr will resume attach if that file is present. If
not, it assumes that the local tenant state is consistent and tries to load the
tenant. If that fails, the tenant transitions into Broken state.
Similar to https://github.com/neondatabase/neon/pull/2395, introduces a state field in Timeline, that's possible to subscribe to.
Adjusts
* walreceiver to not to have any connections if timeline is not Active
* remote storage sync to not to schedule uploads if timeline is Broken
* not to create timelines if a tenant/timeline is broken
* automatically switches timelines' states based on tenant state
Does not adjust timeline's gc, checkpointing and layer flush behaviour much, since it's not safe to cancel these processes abruptly and there's task_mgr::shutdown_tasks that does similar thing.
The 'local' part was always filled in, so that was easy to merge into
into the TimelineInfo itself. 'remote' only contained two fields,
'remote_consistent_lsn' and 'awaits_download'. I made
'remote_consistent_lsn' an optional field, and 'awaits_download' is now
false if the timeline is not present remotely.
However, I kept stub versions of the 'local' and 'remote' structs for
backwards-compatibility, with a few fields that are actively used by
the control plane. They just duplicate the fields from TimelineInfo
now. They can be removed later, once the control plane has been
updated to use the new fields.
It was only None when you queried the status of a timeline with
'timeline_detail' mgmt API call, and it was still being downloaded. You
can check for that status with the 'tenant_status' API call instead,
checking for has_in_progress_downloads field.
Anothere case was if an error happened while trying to get the current
logical size, in a 'timeline_detail' request. It might make sense to
tolerate such errors, and leave the fields we cannot fill in as empty,
None, 0 or similar, but it doesn't make sense to me to leave the whole
'local' struct empty in tht case.
Creates new `pageserver_api` and `safekeeper_api` crates to serve as the
shared dependencies. Should reduce both recompile times and cold compile
times.
Decreases the size of the optimized `neon_local` binary: 380M -> 179M.
No significant changes for anything else (mostly as expected).
