Re: index prefetching

Konstantin Knizhnik <knizhnik@garret.ru>

From: Konstantin Knizhnik <knizhnik@garret.ru>

To: Jim Nasby <jim.nasby@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>

Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2024-01-17T08:04:43Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

aio: io_uring: Trigger async processing for large IOs
- a9ee66881744 19 (unreleased) landed
read stream: Split decision about look ahead for AIO and combining
- 8ca147d582a5 19 (unreleased) landed
read_stream: Only increase read-ahead distance when waiting for IO
- f63ca3379025 19 (unreleased) landed
read_stream: Prevent distance from decaying too quickly
- 6e36930f9aaf 19 (unreleased) landed
Reduce ExecSeqScan* code size using pg_assume()
- b227b0bb4e03 19 (unreleased) cited
Fix rare bug in read_stream.c's split IO handling.
- b421223172a2 19 (unreleased) cited
Fix multiranges to behave more like dependent types.
- 3e8235ba4f9c 17.0 cited
Add EXPLAIN (MEMORY) to report planner memory consumption
- 5de890e3610d 17.0 cited
Optimize nbtree backward scan boundary cases.
- c9c0589fda0e 17.0 cited
Increment xactCompletionCount during subtransaction abort.
- 90c885cdab8b 14.0 cited
Add nbtree Valgrind buffer lock checks.
- 4a70f829d86c 14.0 cited
Add nbtree high key "continuescan" optimization.
- 29b64d1de7c7 12.0 cited
Reduce pinning and buffer content locking for btree scans.
- 2ed5b87f96d4 9.5.0 cited
Teach btree to handle ScalarArrayOpExpr quals natively.
- 9e8da0f75731 9.2.0 cited

On 16/01/2024 11:58 pm, Jim Nasby wrote:
> On 1/16/24 2:10 PM, Konstantin Knizhnik wrote:
>> Amazon RDS is just vanilla Postgres with file system mounted on EBS 
>> (Amazon  distributed file system).
>> EBS provides good throughput but larger latencies comparing with 
>> local SSDs.
>> I am not sure if read-ahead works for EBS.
>
> Actually, EBS only provides a block device - it's definitely not a 
> filesystem itself (*EFS* is a filesystem - but it's also significantly 
> different than EBS). So as long as readahead is happening somewheer 
> above the block device I would expect it to JustWork on EBS.

Thank you for clarification.
Yes, EBS is just block device and read-ahead can be used fir it as for 
any other local device.
There is actually recommendation to increase read-ahead for EBS device 
to reach better performance on some workloads:

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSPerformance.html

So looks like for sequential access pattern manual prefetching at EBS is 
not needed.
But at Neon situation is quite different. May be Aurora Postgres is 
using some other mechanism for speed-up vacuum and seqscan,
but Neon is using Postgres prefetch mechanism for it.