## Problem
We have two No.34 RFC.
## Summary of changes
## Checklist before requesting a review
- [x] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.
## Checklist before merging
- [ ] Do not forget to reformat commit message to not include the above
checklist
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
When a tenant creates a new timeline that they will treat as their
'main' history,
it is awkward to permanently retain an 'old main' timeline as its
ancestor. Currently
this is necessary because it is forbidden to delete a timeline which has
descendents.
## Summary of changes
A new pageserver API is proposed to 'adopt' data from a parent timeline
into
one of its children, such that the link between ancestor and child can
be severed,
leaving the parent in a state where it may then be deleted.
---------
Co-authored-by: Joonas Koivunen <joonas@neon.tech>
We need to shard our Tenants to support larger databases without those
large databases dominating our pageservers and/or requiring dedicated
pageservers.
This RFC aims to define an initial capability that will permit creating
large-capacity databases using a static configuration
defined at time of Tenant creation.
Online re-sharding is deferred as future work, as is offloading layers
for historical reads. However, both of these capabilities would be
implementable without further changes to the control plane or compute:
this RFC aims to define the cross-component work needed to bootstrap
sharding end-to-end.
Usually RFC documents are not modified, but the vast mentions of
"zenith" in early RFC documents make it desirable to update the product
name to today's name, to avoid confusion.
## Problem
Early RFC documents use the old "zenith" product name a lot, which is
not something everyone is aware of after the product was renamed.
## Summary of changes
Replace occurrences of "zenith" with "neon".
Images are excluded.
---------
Co-authored-by: Andreas Scherbaum <andreas@neon.tech>
Enable the pageserver to recover from data corruption events by
implementing a feature to re-apply historic WAL records in parallel to the already
occurring WAL replay.
The feature is outside of the user-visible backup and history story, and
only
serves as a second-level backup for the case that there is a bug in the
pageservers that corrupted the served pages.
The RFC proposes the addition of two new features:
* recover a broken branch from WAL (downtime is allowed)
* a test recovery system to recover random branches to make sure
recovery works
## Problem
Currently we don't have a way to migrate tenants from one pageserver to
another without a risk of gap in availability.
## Summary of changes
This follows on from https://github.com/neondatabase/neon/pull/4919
Migrating tenants between pageservers is essential to operating a
service
at scale, in several contexts:
1. Responding to a pageserver node failure by migrating tenants to other
pageservers
2. Balancing load and capacity across pageservers, for example when a
user expands their
database and they need to migrate to a pageserver with more capacity.
3. Restarting pageservers for upgrades and maintenance
Currently, a tenant may migrated by attaching to a new node,
re-configuring endpoints to use the new node, and then later detaching
from the old node. This is safe once [generation
numbers](025-generation-numbers.md) are implemented, but does meet
our seamless/fast/efficient goals:
Co-authored-by: Christian Schwarz <christian@neon.tech>
This RFC describes a simple scheme to make layer map updates crash
consistent by leveraging the index_part.json in remote storage. Without
such a mechanism, crashes can induce certain edge cases in which broadly
held assumptions about system invariants don't hold.
## Summary
A scheme of logical "generation numbers" for pageservers and their
attachments is proposed, along with
changes to the remote storage format to include these generation numbers
in S3 keys.
Using the control plane as the issuer of these generation numbers
enables strong anti-split-brain
properties in the pageserver cluster without implementing a consensus
mechanism directly
in the pageservers.
## Motivation
Currently, the pageserver's remote storage format does not provide a
mechanism for addressing
split brain conditions that may happen when replacing a node during
failover or when migrating
a tenant from one pageserver to another. From a remote storage
perspective, a split brain condition
occurs whenever two nodes both think they have the same tenant attached,
and both can write to S3. This
can happen in the case of a network partition, pathologically long
delays (e.g. suspended VM), or software
bugs.
This blocks robust implementation of failover from unresponsive
pageservers, due to the risk that
the unresponsive pageserver is still writing to S3.
---------
Co-authored-by: Christian Schwarz <christian@neon.tech>
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
Add infrastructure to dynamically load postgres extensions and shared libraries from remote extension storage.
Before postgres start downloads list of available remote extensions and libraries, and also downloads 'shared_preload_libraries'. After postgres is running, 'compute_ctl' listens for HTTP requests to load files.
Postgres has new GUC 'extension_server_port' to specify port on which 'compute_ctl' listens for requests.
When PostgreSQL requests a file, 'compute_ctl' downloads it.
See more details about feature design and remote extension storage layout in docs/rfcs/024-extension-loading.md
---------
Co-authored-by: Anastasia Lubennikova <anastasia@neon.tech>
Co-authored-by: Alek Westover <alek.westover@gmail.com>
This is a backwards-incompatible change. The new pageserver cannot
read repositories created with an old pageserver binary, or vice
versa.
Simplify Repository to a value-store
------------------------------------
Move the responsibility of tracking relation metadata, like which
relations exist and what are their sizes, from Repository to a new
module, pgdatadir_mapping.rs. The interface to Repository is now a
simple key-value PUT/GET operations.
It's still not any old key-value store though. A Repository is still
responsible from handling branching, and every GET operation comes
with an LSN.
Mapping from Postgres data directory to keys/values
---------------------------------------------------
All the data is now stored in the key-value store. The
'pgdatadir_mapping.rs' module handles mapping from PostgreSQL objects
like relation pages and SLRUs, to key-value pairs.
The key to the Repository key-value store is a Key struct, which
consists of a few integer fields. It's wide enough to store a full
RelFileNode, fork and block number, and to distinguish those from
metadata keys.
'pgdatadir_mapping.rs' is also responsible for maintaining a
"partitioning" of the keyspace. Partitioning means splitting the
keyspace so that each partition holds a roughly equal number of keys.
The partitioning is used when new image layer files are created, so
that each image layer file is roughly the same size.
The partitioning is also responsible for reclaiming space used by
deleted keys. The Repository implementation doesn't have any explicit
support for deleting keys. Instead, the deleted keys are simply
omitted from the partitioning, and when a new image layer is created,
the omitted keys are not copied over to the new image layer. We might
want to implement tombstone keys in the future, to reclaim space
faster, but this will work for now.
Changes to low-level layer file code
------------------------------------
The concept of a "segment" is gone. Each layer file can now store an
arbitrary range of Keys.
Checkpointing, compaction
-------------------------
The background tasks are somewhat different now. Whenever
checkpoint_distance is reached, the WAL receiver thread "freezes" the
current in-memory layer, and creates a new one. This is a quick
operation and doesn't perform any I/O yet. It then launches a
background "layer flushing thread" to write the frozen layer to disk,
as a new L0 delta layer. This mechanism takes care of durability. It
replaces the checkpointing thread.
Compaction is a new background operation that takes a bunch of L0
delta layers, and reshuffles the data in them. It runs in a separate
compaction thread.
Deployment
----------
This also contains changes to the ansible scripts that enable having
multiple different pageservers running at the same time in the staging
environment. We will use that to keep an old version of the pageserver
running, for clusters created with the old version, at the same time
with a new pageserver with the new binary.
Author: Heikki Linnakangas
Author: Konstantin Knizhnik <knizhnik@zenith.tech>
Author: Andrey Taranik <andrey@zenith.tech>
Reviewed-by: Matthias Van De Meent <matthias@zenith.tech>
Reviewed-by: Bojan Serafimov <bojan@zenith.tech>
Reviewed-by: Konstantin Knizhnik <knizhnik@zenith.tech>
Reviewed-by: Anton Shyrabokau <antons@zenith.tech>
Reviewed-by: Dhammika Pathirana <dham@zenith.tech>
Reviewed-by: Kirill Bulatov <kirill@zenith.tech>
Reviewed-by: Anastasia Lubennikova <anastasia@zenith.tech>
Reviewed-by: Alexey Kondratov <alexey@zenith.tech>
