The code in this change was extracted from #2595 (Heikki’s on-demand
download draft PR).
High-Level Changes
- New RemoteLayer Type
- On-Demand Download As An Effect Of Page Reconstruction
- Breaking Semantics For Physical Size Metrics
There are several follow-up work items planned.
Refer to the Epic issue on GitHub: https://github.com/neondatabase/neon/issues/2029
closes https://github.com/neondatabase/neon/pull/3013
Co-authored-by: Kirill Bulatov <kirill@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
New RemoteLayer Type
====================
Instead of downloading all layers during tenant attach, we create
RemoteLayer instances for each of them and add them to the layer map.
On-Demand Download As An Effect Of Page Reconstruction
======================================================
At the heart of pageserver is Timeline::get_reconstruct_data(). It
traverses the layer map until it has collected all the data it needs to
produce the page image. Most code in the code base uses it, though many
layers of indirection.
Before this patch, the function would use synchronous filesystem IO to
load data from disk-resident layer files if the data was not cached.
That is not possible with RemoteLayer, because the layer file has not
been downloaded yet. So, we do the download when get_reconstruct_data
gets there, i.e., “on demand”.
The mechanics of how the download is done are rather involved, because
of the infamous async-sync-async sandwich problem that plagues the async
Rust world. We use the new PageReconstructResult type to work around
this. Its introduction is the cause for a good amount of code churn in
this patch. Refer to the block comment on `with_ondemand_download()`
for details.
Breaking Semantics For Physical Size Metrics
============================================
We rename prometheus metric pageserver_{current,resident}_physical_size to
reflect what this metric actually represents with on-demand download.
This intentionally BREAKS existing grafana dashboard and the cost model data
pipeline. Breaking is desirable because the meaning of this metrics has changed
with on-demand download. See
https://docs.google.com/document/d/12AFpvKY-7FZdR5a4CaD6Ir_rI3QokdCLSPJ6upHxJBo/edit#
for how we will handle this breakage.
Likewise, we rename the new billing_metrics’s PhysicalSize => ResidentSize.
This is not yet used anywhere, so, this is not a breaking change.
There is still a field called TimelineInfo::current_physical_size. It
is now the sum of the layer sizes in layer map, regardless of whether
local or remote. To compute that sum, we added a new trait method
PersistentLayer::file_size().
When updating the Python tests, we got rid of
current_physical_size_non_incremental. An earlier commit removed it from
the OpenAPI spec already, so this is not a breaking change.
test_timeline_size.py has grown additional assertions on the
resident_physical_size metric.
If there are any unexpected ERRORs or WARNs in pageserver.log after test
finishes, fail the test. This requires whitelisting the errors that *are*
expected in each test, and there's also a few common errors that are
printed by most tests, which are whitelisted in the fixture itself.
With this, we don't need the special abort() call in testing mode, when
compaction or GC fails. Those failures will print ERRORs to the logs,
which will be picked up by this new mechanisms.
A bunch of errors are currently whitelisted that we probably shouldn't
be emitting in the first place, but fixing those is out of scope for this
commit, so I just left FIXME comments on them.
This PR replaces the following global variables in the test framework
with fixtures to make tests more configurable. I mainly need this for
the forward compatibility tests (draft in
https://github.com/neondatabase/neon/pull/2766).
```
base_dir
neon_binpath
pg_distrib_dir
top_output_dir
default_pg_version (this one got replaced with a fixture named pg_version)
```
Also, this PR adds more `Path` type where the code implies it.
`test_tenant_relocation` ends up starting a temporary postgres instance with a fixed port. the change makes the port configurable at scripts/export_import_between_pageservers.py and uses that in test_tenant_relocation.
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.
For better ergonomics. I always found it weird that we used UUID to
actually mean a tenant or timeline ID. It worked because it happened
to have the same length, 16 bytes, but it was hacky.
Merge batch_others and batch_pg_regress. The original idea was to
split all the python tests into multiple "batches" and run each batch
in parallel as a separate CI job. However, the batch_pg_regress batch
was pretty short compared to all the tests in batch_others. We could
split batch_others into multiple batches, but it actually seems better
to just treat them as one big pool of tests and use pytest's handle
the parallelism on its own. If we need to split them across multiple
nodes in the future, we could use pytest-shard or something else,
instead of managing the batches ourselves.
Merge test_neon_regress.py, test_pg_regress.py and test_isolation.py
into one file, test_pg_regress.py. Seems more clear to group all
pg_regress-based tests into one file, now that they would all be in
the same directory.
