The logic would incorrectly remove an image layer, if a new image layer
existed, even though the older image layer was still needed by some
delta layers after it. See example given in the comment this adds.
Without this fix, I was getting a lot of "could not find data for key
010000000000000000000000000000000000" errors from GC, with the new test
case being added in PR #1735.
Fixes#707
* Do not apply records with LSN smaller than LSN of cached image in delta layer
* Do not apply records with LSN smaller than LSN of cached image in delta layer
* Traverse frozen layer in get_reconstruct_data in reverse order
* Fix comments on frozen layers.
Note explicitly the order that the layers are in the queue.
* Add fail point to reproduce failpoint iteration error
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
We only checked the cache page version when collecting WAL records in
an in-memory layer, not in a delta layer. Refactor the code so that we
always stop collecting WAL records when we reach a cached materialized
page.
Fix the assertion on the LSN range in
InMemoryLayer::get_value_reconstruct_data. It was supposed to check
that the requested LSN range is within the layer's LSN range, but the
inequality was backwards. That went unnoticed before, because the
caller always passed the layer's start LSN as the requested LSN
range's start LSN, but now we might stop the search earlier, if we have
a cached page version.
Co-authored-by: Konstantin Knizhnik <knizhnik@zenith.tech>
Unlink failure isn't serious on its own, we were about to remove the
file anyway, but it shouldn't happen and could be a symptom of
something more serious.
We just saw "No such file or directory" errors happening from
ephemeral file writeback in staging, and I suspect if we had this
warning in place, we would have seen these warnings too, if the
problem was that the ephemeral file was removed before dropping the
EphemeralFile struct. Next time it happens, we'll have more
information.
We now use a page cache for those, instead of slurping the whole index into
memory.
Fixes https://github.com/zenithdb/zenith/issues/1356
This is a backwards-incompatible change to the storage format, so
bump STORAGE_FORMAT_VERSION.
This introduces two new abstraction layers for I/O:
- Block I/O, and
- Blob I/O.
The BlockReader trait abstracts a file or something else that can be read
in 8kB pages. It is implemented by EphemeralFiles, and by a new
FileBlockReader struct that allows reading arbitrary VirtualFiles in that
manner, utilizing the page cache.
There is also a new BlockCursor struct that works as a cursor over a
BlockReader. When you create a BlockCursor and read the first page using
it, it keeps the reference to the page. If you access the same page again,
it avoids going to page cache and quickly returns the same page again.
That can save a lot of lookups in the page cache if you perform multiple
reads.
The Blob-oriented API allows reading and writing "blobs" of arbitrary
length. It is a layer on top of the block-oriented API. When you write
a blob with the write_blob() function, it writes a length field
followed by the actual data to the underlying block storage, and
returns the offset where the blob was stored. The blob can be
retrieved later using the offset.
Finally, this replaces the I/O code in image-, delta-, and in-memory
layers to use the new abstractions. These replace the 'bookfile'
crate.
This is a backwards-incompatible change to the storage format.
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>
With a Mutex, only one thread could read from the layer at a time. I did
some ad hoc profiling with pgbench and saw that a fair amout of time was
spent blocked on these Mutexes.
It doesn't make much sense to compare TimelineMetadata structs with
< or >. But we depended on that in the remote storage upload code,
so replace BTreeSets with Vecs there.
Since commit fdd987c3ad, it was only used in InMemoryLayers. Let's
just "inline" the code into InMemoryLayer itself.
I originally did this as part of a bigger PR (#1267). With that PR,
one in-memory layer, and one ephemeral file, would hold page versions
belonging to multiple segments. Currently, PageVersions can only hold
versions for a single segment, so that would need to be changed.
Rather than modify PageVersions to support that, just remove it
altogether.
* Freeze vectors at the same end LSN
* Fix calculation of last LSN for inmem layer
* Do not advance disk_consistent_lsn is no open layer was evicted
* Fix calculation of freeze_end_lsn
* Let start_lsn be larger than oldest_pending_lsn
* Rename 'oldest_pending_lsn' and 'last_lsn', add comments.
* Fix future_layerfiles test
* Update comments conserning olest_lsn
* Update comments conserning olest_lsn
Co-authored-by: Heikki Linnakangas <heikki@zenith.tech>
