## Problem
Part of LKB-379
The pageserver connstrings are updated in the postmaster and then
there's a hook to propagate it to the shared memory of all backends.
However, the shard stripe doesn't. This would cause problems during
shard splits:
* the compute has active reads/writes
* shard split happens and the cplane applies the new config (pageserver
connstring + stripe size)
* pageserver connstring will be updated immediately once the postmaster
receives the SIGHUP, and it will be copied over the the shared memory of
all other backends.
* stripe size is a normal GUC and we don't have special handling around
that, so if any active backend has ongoing txns the value won't be
applied.
* now it's possible for backends to issue requests based on the wrong
stripe size; what's worse, if a request gets cached in the prefetch
buffer, it will get stuck forever.
## Summary of changes
To make sure it aligns with the current default in storcon.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
One PG tenant may write too fast and overwhelm the PS. The other tenants
sharing the same PSs will get very little bandwidth.
We had one experiment that two tenants sharing the same PSs. One tenant
runs a large ingestion that delivers hundreds of MB/s while the other
only get < 10 MB/s.
## Summary of changes
Rate limit how fast PG can generate WALs. The default is -1. We may
scale the default value with the CPU count. Need to run some experiments
to verify.
## How is this tested?
CI.
PGBench. No limit first. Then set to 1 MB/s and you can see the tps
drop. Then reverted the change and tps increased again.
pgbench -i -s 10 -p 55432 -h 127.0.0.1 -U cloud_admin -d postgres
pgbench postgres -c 10 -j 10 -T 6000000 -P 1 -b tpcb-like -h 127.0.0.1
-U cloud_admin -p 55432
progress: 33.0 s, 986.0 tps, lat 10.142 ms stddev 3.856 progress: 34.0
s, 973.0 tps, lat 10.299 ms stddev 3.857 progress: 35.0 s, 1004.0 tps,
lat 9.939 ms stddev 3.604 progress: 36.0 s, 984.0 tps, lat 10.183 ms
stddev 3.713 progress: 37.0 s, 998.0 tps, lat 10.004 ms stddev 3.668
progress: 38.0 s, 648.9 tps, lat 12.947 ms stddev 24.970 progress: 39.0
s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 40.0 s, 0.0 tps, lat
0.000 ms stddev 0.000 progress: 41.0 s, 0.0 tps, lat 0.000 ms stddev
0.000 progress: 42.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress:
43.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 44.0 s, 0.0 tps,
lat 0.000 ms stddev 0.000 progress: 45.0 s, 0.0 tps, lat 0.000 ms stddev
0.000 progress: 46.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress:
47.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 48.0 s, 0.0 tps,
lat 0.000 ms stddev 0.000 progress: 49.0 s, 347.3 tps, lat 321.560 ms
stddev 1805.633 progress: 50.0 s, 346.8 tps, lat 9.898 ms stddev 3.809
progress: 51.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 52.0 s,
0.0 tps, lat 0.000 ms stddev 0.000 progress: 53.0 s, 0.0 tps, lat 0.000
ms stddev 0.000 progress: 54.0 s, 0.0 tps, lat 0.000 ms stddev 0.000
progress: 55.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 56.0 s,
0.0 tps, lat 0.000 ms stddev 0.000 progress: 57.0 s, 0.0 tps, lat 0.000
ms stddev 0.000 progress: 58.0 s, 0.0 tps, lat 0.000 ms stddev 0.000
progress: 59.0 s, 0.0 tps, lat 0.000 ms stddev 0.000 progress: 60.0 s,
0.0 tps, lat 0.000 ms stddev 0.000 progress: 61.0 s, 0.0 tps, lat 0.000
ms stddev 0.000 progress: 62.0 s, 0.0 tps, lat 0.000 ms stddev 0.000
progress: 63.0 s, 494.5 tps, lat 276.504 ms stddev 1853.689 progress:
64.0 s, 488.0 tps, lat 20.530 ms stddev 71.981 progress: 65.0 s, 407.8
tps, lat 9.502 ms stddev 3.329 progress: 66.0 s, 0.0 tps, lat 0.000 ms
stddev 0.000 progress: 67.0 s, 0.0 tps, lat 0.000 ms stddev 0.000
progress: 68.0 s, 504.5 tps, lat 71.627 ms stddev 397.733 progress: 69.0
s, 371.0 tps, lat 24.898 ms stddev 29.007 progress: 70.0 s, 541.0 tps,
lat 19.684 ms stddev 24.094 progress: 71.0 s, 342.0 tps, lat 29.542 ms
stddev 54.935
Co-authored-by: Haoyu Huang <haoyu.huang@databricks.com>
I believe the explicit memory fence instructions are
unnecessary. Performing a store with Release ordering makes all the
previous non-atomic writes visible too. Per rust docs for Ordering::Release
( https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html#variant.Release):
> When coupled with a store, all previous operations become ordered
> before any load of this value with Acquire (or stronger)
> ordering. In particular, all previous writes become visible to all
> threads that perform an Acquire (or stronger) load of this value.
>
> ...
>
> Corresponds to memory_order_release in C++20.
The "all previous writes" means non-atomic writes too. It's not very
clear from that text, but the C++20 docs that it links to is more
explicit about it:
> All memory writes (including non-atomic and relaxed atomic) that
> happened-before the atomic store from the point of view of thread A,
> become visible side-effects in thread B. That is, once the atomic
> load is completed, thread B is guaranteed to see everything thread A
> wrote to memory.
In addition to removing the fence instructions, fix the comments on
each atomic Acquire operation to point to the correct Release
counterpart. We had such comments but they had gone out-of-date as
code has moved.
All the callers did that previously. So rather than document that the
caller needs to do it, just do it in start_neon_io_request() straight
away. (We might want to revisit this if we get codepaths where the C
code submits multiple IO requests as a batch. In that case, it would
be more efficient to fill all the request slots first and only send
one notification to the pipe for all of them)
All the code talks about "request slots", better to make the struct
name reflect that. The "Handle" term was borrowed from Postgres v18
AIO implementation, from the similar handles or slots used to submit
IO requests from backends to worker processes. But even though the
idea is similar, it's a completely separate implementation and there's
nothing else shared between them than the very high level
design.
When a function is owned by a superuser (bootstrap user or otherwise),
we consider it safe to run it. Only a superuser could have installed it,
typically from CREATE EXTENSION script: we trust the code to execute.
## Problem
This is intended to solve running pg_graphql Event Triggers
graphql_watch_ddl and graphql_watch_drop which are executing the secdef
function graphql.increment_schema_version().
## Summary of changes
Allow executing Event Trigger function owned by a superuser and with
SECURITY DEFINER properties. The Event Trigger code runs with superuser
privileges, and we consider that it's fine.
---------
Co-authored-by: Tristan Partin <tristan.partin@databricks.com>
This greatly reduces the cases where we make a request to the
pageserver with a very recent LSN. Those cases are slow because the
pageserver needs to wait for the WAL to arrive. This speeds up the
Postgres pg_regress and isolation tests greatly.
## Problem
See [Slack
Channel](https://databricks.enterprise.slack.com/archives/C091LHU6NNB)
Dropping connection without resetting prefetch state can cause
request/response mismatch.
And lack of check response correctness in communicator_prefetch_lookupv
can cause data corruption.
## Summary of changes
1. Validate response before assignment to prefetch slot.
2. Consume prefetch requests before sending any other requests.
---------
Co-authored-by: Kosntantin Knizhnik <konstantin.knizhnik@databricks.com>
Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
With this refactoring, the Rust code deals with one giant array of
requests, and doesn't know that it's sliced up per backend
process. The C code is now responsible for slicing it up.
This also adds code to complete old IOs at backends start that were
started and left behind by a previous session. That was a little more
straightforward to do with the refactoring, which is why I tackled it
now.
This doesn't do anything interesting yet, but demonstrates linking Rust
code to the neon Postgres extension, so that we can review and test
drive just the build process changes independently.
