## Problem
The vectored read path holds the layer map lock while visiting a
timeline.
## Summary of changes
* Rework the fringe order to hold `Layer` on `Arc<InMemoryLayer>`
handles instead of descriptions that are resolved by the layer map at
the time of read. Note that previously `get_values_reconstruct_data` was
implemented for the layer description which already knew the lsn range
for the read. Now it is implemented on the new `ReadableLayer` handle
and needs to get the lsn range as an argument.
* Drop the layer map lock after updating the fringe.
Related https://github.com/neondatabase/neon/issues/6833
## Problem
When vectored get encountered a portion of the key range that could
not be mapped to any layer in the current timeline it would incorrectly
bail out of the current timeline. This is incorrect since we may have
had layers queued for a visit in the fringe.
## Summary of changes
* Add a repro unit test
* Remove the early bail out path
* Simplify range search return value
This PR introduces a new vectored implementation of the read path.
The search is basically a DFS if you squint at it long enough.
LayerFringe tracks the next layers to visit and acts as our stack.
Vertices are tuples of (layer, keyspace, lsn range). Continuously
pop the top of the stack (most recent layer) and do all the reads
for one layer at once.
The search maintains a fringe (`LayerFringe`) which tracks all the
layers that intersect the current keyspace being searched. Continuously
pop the top of the fringe (layer with highest LSN) and get all the data
required from the layer in one go.
Said search is done on one timeline at a time. If data is still required for
some keys, then search the ancestor timeline.
Apart from the high level layer traversal, vectored variants have been
introduced for grabbing data from each layer type. They still suffer from
read amplification issues and that will be addressed in a different PR.
You might notice that in some places we duplicate the code for the
existing read path. All of that code will be removed when we switch
the non-vectored read path to proxy into the vectored read path.
In the meantime, we'll have to contend with the extra cruft for the sake
of testing and gentle releasing.
## Problem
There's no efficient way of querying the layer map for a range.
## Summary of changes
Introduce a range query for the layer map (`LayerMap::range_search`).
There's two broad steps to it:
1. Find all coverage changes for layers that intersect the queried range
(see `LayerCoverage::range_overlaps`).
The slightly tricky part is dealing with the start of the range. We can
either be aligned with a layer or not and we need
to treat these cases differently.
2. Iterate over the coverage changes and collect the result. For this we
use a two pointer approach: the trailing pointer tracks the start of the
current range (current location in the key space) and the forward
pointer tracks the next coverage change.
Plugging the range search into the read path is deferred to a future PR.
## Performance
I adapted the layer map benchmarks on a local branch. Range searches are
between 2x and 2.5x slower than point searches. That's in line with what I
expected since we query thelayer map twice.
Since `Timeline::get` will proxy to `Timeline::get_vectored` we can
special case the one element layer map range search
at that point.
1. Introduce a naive `Timeline::get_vectored` implementation
The return type is intended to be flexible enough for various types of
callers. We return the pages in a map keyed by `Key` such that the
caller doesn't have to map back to the key if it needs to know it. Some
callers can ignore errors
for specific pages, so we return a separate `Result<Bytes,
PageReconstructError>` for each page and an overarching
`GetVectoredError` for API misuse. The overhead of the mapping will be
small and bounded since we enforce a maximum key count for the
operation.
2. Use the `get_vectored` API for SLRU segment reconstruction and image
layer creation.
Implement a new `struct Layer` abstraction which manages downloadness
internally, requiring no LayerMap locking or rewriting to download or
evict providing a property "you have a layer, you can read it". The new
`struct Layer` provides ability to keep the file resident via a RAII
structure for new layers which still need to be uploaded. Previous
solution solved this `RemoteTimelineClient::wait_completion` which lead
to bugs like #5639. Evicting or the final local deletion after garbage
collection is done using Arc'd value `Drop`.
With a single `struct Layer` the closed open ended `trait Layer`, `trait
PersistentLayer` and `struct RemoteLayer` are removed following noting
that compaction could be simplified by simply not using any of the
traits in between: #4839.
The new `struct Layer` is a preliminary to remove
`Timeline::layer_removal_cs` documented in #4745.
Preliminaries: #4936, #4937, #5013, #5014, #5022, #5033, #5044, #5058,
#5059, #5061, #5074, #5103, epic #5172, #5645, #5649. Related split off:
#5057, #5134.
In the quest to solve #4745 by moving the download/evictedness to be
internally mutable factor of a Layer and get rid of `trait
PersistentLayer` at least for prod usage, `layer_removal_cs`, we present
some misc cleanups.
---------
Co-authored-by: Dmitry Rodionov <dmitry@neon.tech>
In #4743, we'd like to convert the read path to use `async` rust. In
preparation of that, this PR switches some functions that are calling
lower level functions like `BlockReader::read_blk`,
`BlockCursor::read_blob`, etc into `async`. The PR does not switch all
functions however, and only focuses on the ones which are easy to
switch.
This leaves around some async functions that are (currently)
unnecessarily `async`, but on the other hand it makes future changes
smaller in diff.
Part of #4743 (but does not completely address it).
## Problem
`cargo +nightly doc` is giving a lot of warnings: broken links, naked
URLs, etc.
## Summary of changes
* update the `proc-macro2` dependency so that it can compile on latest
Rust nightly, see https://github.com/dtolnay/proc-macro2/pull/391 and
https://github.com/dtolnay/proc-macro2/issues/398
* allow the `private_intra_doc_links` lint, as linking to something
that's private is always more useful than just mentioning it without a
link: if the link breaks in the future, at least there is a warning due
to that. Also, one might enable
[`--document-private-items`](https://doc.rust-lang.org/cargo/commands/cargo-doc.html#documentation-options)
in the future and make these links work in general.
* fix all the remaining warnings given by `cargo +nightly doc`
* make it possible to run `cargo doc` on stable Rust by updating
`opentelemetry` and associated crates to version 0.19, pulling in a fix
that previously broke `cargo doc` on stable:
https://github.com/open-telemetry/opentelemetry-rust/pull/904
* Add `cargo doc` to CI to ensure that it won't get broken in the
future.
Fixes#2557
## Future work
* Potentially, it might make sense, for development purposes, to publish
the generated rustdocs somewhere, like for example [how the rust
compiler does
it](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/index.html).
I will file an issue for discussion.
## Problem
ref https://github.com/neondatabase/neon/issues/4373
## Summary of changes
A step towards immutable layer map. I decided to finish the refactor
with this new approach and apply
https://github.com/neondatabase/neon/pull/4455 on this patch later.
In this PR, we moved all modifications of the layer map to one place
with semantic operations like `initialize_local_layers`,
`finish_compact_l0`, `finish_gc_timeline`, etc, which is now part
of `LayerManager`. This makes it easier to build new features upon
this PR:
* For immutable storage state refactor, we can simply replace the layer
map with `ArcSwap<LayerMap>` and remove the `layers` lock. Moving
towards it requires us to put all layer map changes in a single place as
in https://github.com/neondatabase/neon/pull/4455.
* For manifest, we can write to manifest in each of the semantic
functions.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
## Problem
part of https://github.com/neondatabase/neon/pull/4340
## Summary of changes
Remove LayerDescriptor and remove `todo!`. At the same time, this PR
adds `AsLayerDesc` trait for all persistent layers and changed
`LayerFileManager` to have a generic type. For tests, we are now using
`LayerObject`, which is a wrapper around `PersistentLayerDesc`.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
I was reading the code of the page server today and found these minor
things that I thought could be cleaned up.
## Summary of changes
* remove a redundant indentation layer and continue in the flushing loop
* use the builtin `PartialEq` check instead of hand-rolling a `range_eq`
function
* Add a missing `>` to a prominent doc comment
## Problem
part of https://github.com/neondatabase/neon/issues/4392, continuation
of https://github.com/neondatabase/neon/pull/4408
## Summary of changes
This PR removes all layer objects from LayerMap and moves it to the
timeline struct. In timeline struct, LayerFileManager maps a layer
descriptor to a layer object, and it is stored in the same RwLock as
LayerMap to avoid behavior difference.
Key changes:
* LayerMap now does not have generic, and only stores descriptors.
* In Timeline, we add a new struct called layer mapping.
* Currently, layer mapping is stored in the same lock with layer map.
Every time we retrieve data from the layer map, we will need to map the
descriptor to the actual object.
* Replace_historic is moved to layer mapping's replace, and the return
value behavior is different from before. I'm a little bit unsure about
this part and it would be good to have some comments on that.
* Some test cases are rewritten to adapt to the new interface, and we
can decide whether to remove it in the future because it does not make
much sense now.
* LayerDescriptor is moved to `tests` module and should only be intended
for unit testing / benchmarks.
* Because we now have a usage pattern like "take the guard of lock, then
get the reference of two fields", we want to avoid dropping the
incorrect object when we intend to unlock the lock guard. Therefore, a
new set of helper function `drop_r/wlock` is added. This can be removed
in the future when we finish the refactor.
TODOs after this PR: fully remove RemoteLayer, and move LayerMapping to
a separate LayerCache.
all refactor PRs:
```
#4437 --- #4479 ------------ #4510 (refactor done at this point)
\-- #4455 -- #4502 --/
```
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
part of https://github.com/neondatabase/neon/issues/4392
## Summary of changes
This PR adds a new HashMap that maps persistent layer desc to the layer
object *inside* LayerMap. Originally I directly went towards adding such
layer cache in Timeline, but the changes are too many and cannot be
reviewed as a reasonably-sized PR. Therefore, we take this intermediate
step to change part of the codebase to use persistent layer desc, and
come up with other PRs to move this hash map of layer desc to the
timeline struct.
Also, file_size is now part of the layer desc.
---------
Signed-off-by: Alex Chi <iskyzh@gmail.com>
Co-authored-by: bojanserafimov <bojan.serafimov7@gmail.com>
This reverts commit 732acc5.
Reverted PR: #3869
As noted in PR #4094, we do in fact try to insert duplicates to the
layer map, if L0->L1 compaction is interrupted. We do not have a proper
fix for that right now, and we are in a hurry to make a release to
production, so revert the changes related to this to the state that we
have in production currently. We know that we have a bug here, but
better to live with the bug that we've had in production for a long
time, than rush a fix to production without testing it in staging first.
Cc: #4094, #4088
## Describe your changes
## Issue ticket number and link
#3673
## Checklist before requesting a review
- [ ] 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.
---------
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
in prev implementation, an `ok_or_else(...)?` is used to cause a
"precondition error" on LayerMap::replace, however we only see this
particular error if an L0 for which replace fails is not in the layermap
because it is not in `l0_delta_layers`. changes or fixes this to be
Replacement::NotFound instead, making it more clear that an error would
only be raised for actual preconditions, like trying to replace layer
with completly unrelated layer.
This changes the way we compare `Arc<dyn PersistentLayer>` in Timeline's
`LayerMap` not to use `Arc::ptr_eq` which has been witnessed in
development of #3557 to yield wrong results. It gives wrong results
because it compares fat pointers, which are `(object, vtable)` tuples
for `dyn Trait` and there are no guarantees that the `vtable`s are
unique. As in there were multiple vtables for `RemoteLayer` which is why
the comparison failed in #3557.
This is a known issue in rust, clippy warns against it and rust std
might be moving to the solution which has been reproduced on this PR:
compare only object pointers by "casting out" the vtable pointer.
Cc: #3486
Adds a method to replace a particular layer from the LayerMap for the
purposes of remote layer download and layer eviction. In those use cases
read lock on layer map needs to be released after initial search, but
other operations could modify layermap before replacing thread gets to
run.
Co-authored-by: bojanserafimov <bojan.serafimov7@gmail.com>
While @bojanserafimov is still working on best replacement of R-Tree in
layer_map.rs there is obvious pitfall in the current `search` method
implementation: is returns delta layer even if there is image layer if
greater LSN. I think that it should be fixed.
refactor: use new type LayerFileName when referring to layer file names in PathBuf/RemotePath
Before this patch, we would sometimes carry around plain file names in
`Path` types and/or awkwardly "rebase" paths to have a unified
representation of the layer file name between local and remote.
This patch introduces a new type `LayerFileName` which replaces the use
of `Path` / `PathBuf` / `RemotePath` in the `storage_sync2` APIs.
Instead of holding a string, it contains the parsed representation of
the image and delta file name.
When we need the file name, e.g., to construct a local path or
remote object key, we construct the name ad-hoc.
`LayerFileName` is also serde {Dese,Se}rializable, and in an initial
version of this patch, it was supposed to be used directly inside
`IndexPart`, replacing `RemotePath`.
However,
commit 3122f3282f
Ignore backup files (ones with .n.old suffix) in download_missing
fixed handling of `*.old` backup file names in IndexPart, and we need
to carry that behavior forward.
The solution is to remove `*.old` backup files names during
deserialization. When we re-serialize the IndexPart, the `*.old` file
will be gone.
This leaks the `.old` file in the remote storage, but makes it safe
to clean it up later.
There is additional churn by a preliminary refactoring that got squashed
into this change:
split off LayerMap's needs from trait Layer into super trait
That refactoring renames `Layer` to `PersistentLayer` and splits off a subset
of the functions into a super-trait called `Layer`.
The upser trait implements just the functions needed by `LayerMap`, whereas
`PersisentLayer` adds the context of the pageserver.
The naming is imperfect as some functions that reside in `PersistentLayer`
have nothing persistence-specific to it. But it's a step in the right direction.
Lookups in the R-tree call the "envelope" function for every comparison,
and our envelope function isn't very cheap, so that overhead adds up.
Create the envelope once, when the layer is inserted into the tree, and
store it along with the layer. That uses some more memory per layer, but
that's not very significant.
Speeds up the search operation 2x
Replace the layer array and linear search with R-tree
So far, the in-memory layer map that holds information about layer
files that exist, has used a simple Vec, in no particular order, to
hold information about all the layers. That obviously doesn't scale
very well; with thousands of layer files the linear search was
consuming a lot of CPU. Replace it with a two-dimensional R-tree, with
Key and LSN ranges as the dimensions.
For the R-tree, use the 'rstar' crate. To be able to use that, we
convert the Keys and LSNs into 256-bit integers. 64 bits would be
enough to represent LSNs, and 128 bits would be enough to represent
Keys. However, we use 256 bits, because rstar internally performs
multiplication to calculate the area of rectangles, and the result of
multiplying two 128 bit integers doesn't necessarily fit in 128 bits,
causing integer overflow and, if overflow-checks are enabled,
panic. To avoid that, we use 256 bit integers.
Add a performance test that creates a lot of layer files, to
demonstrate the benefit.
