pgaddict

7 ms·

1.
by pgaddict 1mo ago
OMG, please no. Make it very obvious which of the three possible behaviors is active. Trying to compress that into just two options is utterly confusing and hard to interpret, especially when it depends on what's the current system the
2.
by pgaddict 4mo ago
I really wish they clearly documented the parameters used by each of the databases (or are we expected to dig those out of the .rs sources somehow?), and actual versions used (saying "Postgres" is ambiguous, it could be 14 or 18 -
3.
by pgaddict 4mo ago
Interesting paper. I only started reading / digesting it, but: - I'm not sure how to interpret the Figure 1. It says "Flash writes (KB) per page", but it doesn't really say which page sizes were used. AFAIK MySQL ha
4.
by pgaddict 6mo ago
So why does it happen only with hugepages? Is the extra overhead / TLB pressure enough to trigger the issue in some way? Of is it because the regular pages get swapped out (which hugepages can't be)?
5.
by pgaddict 7mo ago
True. Unfortunately it's what index scans in Postgres do right now - it's the last "major" scan type not supporting some sort of prefetch (posix_fadvise or AIO). We're working on it, hopefully it'll get into PG
6.
by pgaddict 7mo ago
To the best of my knowledge, yes. Unfortunately the details of how it was calculated in ~2000 seem to be lost, but the person who did that described he did it like this. It's possible we forgot some important details, of course, but th
7.
by pgaddict 7mo ago
Damn, I copied the wrong command. I wanted to copy this one: fio --filename=/dev/md127 --direct=1 --rw=randread --bs=8k --ioengine=io_uring --iodepth=1 --runtime=120 --numjobs=1 --time_based --group_reporting --name=iops-test-job
8.
by pgaddict 7mo ago
Good idea. It's an interesting historical question - when we picked 4.0 as the default ~25 years ago, how close was is to the calculated value? I was asking that myself. Unfortunately I don't have a machine with traditional HDD in
9.
by pgaddict 7mo ago
Good point, I should have included that (the linked pgsql-hackers thread have some of this information, at least). I've observed exactly this behavior on a wide range of hardware / environments, it's not very specific to part
10.
by pgaddict 7mo ago
There probably is some additional inefficiency when reading pages randomly (compared to sequential reads), but most of the difference is at the storage level. That is, SSDs can handle a lot of random I/O, but it's nowhere close to
11.
by pgaddict 10mo ago
AFAIK these two joins are exactly the same once you get past the parsing. It's just a different way to write an inner join. It's translated into the same AST and so there's no difference in planning/execution.
12.
by pgaddict 10mo ago
That is part of the key idea, yes. It's more elaborate, because it can split the aggregate - it can do part of it before the join, and finalize it after the join. Similarly to what we do for parallel queries. As for indexes, it can hel
13.
by pgaddict 10mo ago
It's not about not knowing about an optimization. The challenge is to know when to apply it, so that it does not cause regressions for cases that can't benefit from it. It may be less risky in specialized systems, like BI systems
14.
by pgaddict 11mo ago
IMHO the whole point of Qubes is that it does not do the compartmentalization at the level of individual applications, but groups of applications. Otherwise you'd need to very clearly specify how/when exactly the applications ca
15.
by pgaddict 1y ago
I'm not sure what exactly you mean by "thread" here. Postgres is not thread-based - there are people working on that, but for now it's all processes. Some of these limitations are mostly due to Postgres design, no doubt
16.
by pgaddict 1y ago
I believe there are reasons why e.g. io_uring could be inherently slower in some cases, and I tried to point some of those out. With io_uring everything happens in the backend process, and so consumes some of the CPU time that might otherwi
17.
by pgaddict 1y ago
Debian 12/13, with kernel 6.15. Sorry, should have mentioned that in the blog post.
18.
by pgaddict 1y ago
> Right now async IO is used for sequential scans and bitmap scans, not for index scans. My initial guess would be that it mostly helps for complex queries (that use multiple indexes, so bitmap scans) and unoptimized queries (sequential
19.
by pgaddict 1y ago
I did a lot of tests comparing the io_method choices, and I'm yet to see a realistic query where it makes a significant difference of more than a couple percent (in either direction). I'm sure it's possible to construct such
20.
by pgaddict 1y ago
The funny thing is the local communist newspaper "Red Truth" (as if there were non-communist ones, ...) published a review of LOTR in 1977, in which they pretty much took the side of the Mordor. (It might be a made-up joke from th
21.
by pgaddict 1y ago
The toaster mention reminded me of this: https://www.youtube.com/watch?v=LRq_SAuQDec This is how "talking to AI" feels like for anything mildly complex.
22.
by pgaddict 1y ago
I've been involved in a couple of those cases, where a large company ran into an issue, and chose to solve it by migrating to something else. And while the issues certainly exist (and are being addressed), the technical reasons often t
23.
by pgaddict 2y ago
I only noticed the jerky scrolling on pages with a lot of images, particularly hires + CSS effects (blur etc.). Everything else feels OK to me (I'm sure it could be smoother, but it's not too bad so I haven't noticed). For ba
24.
by pgaddict 2y ago
Thanks for the clarification.
25.
by pgaddict 2y ago
I occasionally see stutters too, even with Full HD video. Or more precisely, mplayer complained about slowness and having to drop frames. It often helped to actually give the VM more cores (not just the default 2), but sometimes it was due
26.
by pgaddict 2y ago
Not sure what "mpv" means in this context, but this reminds me the one actual pet peeve I have with Qubes - video/audio calls just don't work for me. It either doesn't work or the audio quality is really poor. I&#x2
27.
by pgaddict 2y ago
Weird. Multiple people submitted HCL for X260, and not a single one mentions issues with sleep. https://www.qubes-os.org/hcl/ When I had similar issues in the past, I posted a question either to the mailing list or for
28.
by pgaddict 2y ago
I'm using Qubes OS as my primary for years - I think I started with the 2.0 release in 2014 (I might have tried/used the 1.0 release, I don't recall.) and I was immediately hooked. I understand the usual story is that the goa
29.
by pgaddict 2y ago
I guess it's this MySQL bug: https://bugs.mysql.com/bug.php?id=101369 which seems to have stalled after request ti sign an OCA. Anyway, I have no idea what would it take to do something like that in Postgres, I'm
30.
by pgaddict 2y ago
Interesting question. I think most optimizations described in the BOLT paper are fairly hardware agnostic - branch prediction does not depend the architecture, etc. But I'm not an expert on microarchitectures.

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