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AndresFreundTec's profile
Andres Freund (Tech)
Andres Freund (Tech)
Andres Freund (Tech)
@AndresFreundTec

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Andres Freund (Tech)

@AndresFreundTec

Postgres developer, working at Microsoft. Also: politics nerd, expat German in the US. Account for tech related things. For politics: @AndresFreundPol

San Francisco, CA
Joined August 2017

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    Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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    I wonder when this "databases are nearly always bottlenecked on IO" perception finally is going to die. I think it's been false for > 50% of instances for at least 15 years. And it's just plainly wrong when we can have small-ish servers with >16 internal NVMe drives.

    10:47 AM - 24 Feb 2020
    • 11 Retweets
    • 43 Likes
    • Yosi Attias davidfetter Jim Nasby Glauber Costa Mark Callaghan Randy Zwitch Chris Ellis Jeremy Schneider Ivan Kozik
    9 replies 11 retweets 43 likes
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      2. Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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        Most databases are going to be bottlenecked on CPU well before they handle ~50GB/s. And it's gotten considerably more likely with the spectre/meltdown mitigations. Especially OLTP is pretty syscall heavy.

        6 replies 0 retweets 13 likes
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      3. Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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        A lot of this perception was formed when there were no SSDs, and memory was so scarce that it'd never fit a meaningful percentage of ones workload. But especially the latter has been wrong for a looong time. A *lot* of databases are in ~100MB - ~10GB range.

        2 replies 2 retweets 14 likes
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      4. End of conversation
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      2. Mark Callaghan‏ @MarkCallaghanDB Feb 24
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        Replying to @AndresFreundTec

        Even more CPU used if DBMS does checksum and/or decompress after each storage read

        1 reply 0 retweets 2 likes
      3. Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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        Replying to @MarkCallaghanDB

        True. It's impressive though what kind of decompression bandwidth e.g. lz4 can have. It's feasible to reach >2GB/s even for some database uses (where typically the number of blocks decompressed at once is small-ish).

        2 replies 0 retweets 1 like
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      2. Álvaro Hernández‏ @ahachete Feb 24
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        Replying to @AndresFreundTec

        Who has NVMe disks for their production workloads? In the cloud few, as they are mostly ephemeral. And since the cloud has an increasing market share, my answer to your Q is "definitely not soon". It could actually be increasing in the opposite direction with faster CPUs.

        2 replies 0 retweets 2 likes
      3. Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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        Replying to @ahachete

        Even if you don't, you have access to high bandwidth, very parallel, but higher latency storage.

        1 reply 0 retweets 0 likes
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      2. Darafei Komяpa Praliaskouski‏ @komzpa Feb 24
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        Replying to @AndresFreundTec

        Who has this perception? Postgres often crawls hundreds of kb/s for me with 100% cpu load, toasting, detoasting and especially calling gist penalty in an almost-O(N^2) loop when trying to build it.

        1 reply 0 retweets 0 likes
      3. Andres Freund (Tech)‏ @AndresFreundTec Feb 24
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        Replying to @komzpa

        Most databases don't run postgis. I can saturate 6GB/s on my laptop with today's postgres for some workloads. We really should throw out pglz and replace it with lz4 by default. But I'm currently working on other 'really should's.

        1 reply 0 retweets 6 likes
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      1. Magnus Hagander‏ @magnushagander Feb 25
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        Replying to @AndresFreundTec

        I read that and agreed. But then there are the systems in "enterprise installs" that are installed in a VMware machine with insufficient ram sitting on top of a massively overbooked SAN. And they are most definitely limited by IO and in my experience are in a big majority.

        0 replies 0 retweets 5 likes
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      1. Jonah H. Harris‏ @jonahharris Feb 24
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        Replying to @AndresFreundTec @TanelPoder

        Everything is a CPU problem

        0 replies 0 retweets 4 likes
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