4 ms·

Well, you are just confirming parent's affirmation. Not everybody uses the cloud. A database like PostgreSQL very much has local file storage usage and hence ve

by ldng 6y ago

Well, you are just confirming parent's affirmation. Not everybody uses the cloud. A database like PostgreSQL very much has local file storage usage and hence very high page cache usage. Or am I missing something ?

refulgentis 6y ago
No - the post carefully lays out that client devices _also_ are dependent on anon page cache. Additionally, TFA has massive impressively statistics for client-side devices, as a cousin comment notes.
- ldng 6y ago
  To me the TFA I've read says they've tested what is convenient for them: cloud compute node, chromebook (which are not desktop in the traditional sens) and phone. Which is fine since it suits their needs. But I maintain it needs more independant testing, on good-old-not-cloud-server, especially databases (which are not client-side devices). It may very well be that it is positive for that workoad too. Or not. That is all I'm saying.
  - notriddle 6y ago
    > But I maintain it needs more independant testing, on good-old-not-cloud-server, especially databases Don't a lot of databases bypass the page cache for their payload data anyhow?
    - jeffbee 6y ago
      Universally. The kernel's page cache is the very last thing that a database operator wants.
      - yuzhao 6y ago
        I'm one of the Google engineers who work on multigenerational LRU. The kernel page cache doesn't know better than databases themselves when it comes to what to cache. All high performance databases do this in user space, and they use AIO with direct IO or the latest io_uring to bypass the kernel page cache. Modern cloud (distributed) file systems do the same, including GFS: https://en.wikipedia.org/wiki/Google_File_System https://en.wikipedia.org/wiki/Google_File_System And speaking of io_uring, check this out to see how much improvement when copying without going through page cache: https://wheybags.com/blog/wcp.html https://wheybags.com/blog/wcp.html
    - jandrewrogers 6y ago
      Yes. Bypassing the kernel cache is a major optimization used by virtually all databases that are serious about prioritizing performance. It won't add anything to the top end of database engine performance. However, there are plenty of databases that do not prioritize performance which could benefit, including most open source ones.
    - ldng 6y ago
      It is not as simple as that : https://www.pgcon.org/events/pgcon_2020/schedule/session/152-asynchronous-io-for-postgresql/ https://www.pgcon.org/events/pgcon_2020/schedule/session/152...

by ldng 6y ago

refulgentis 6y ago

No - the post carefully lays out that client devices _also_ are dependent on anon page cache. Additionally, TFA has massive impressively statistics for client-side devices, as a cousin comment notes.

ldng 6y ago
To me the TFA I've read says they've tested what is convenient for them: cloud compute node, chromebook (which are not desktop in the traditional sens) and phone. Which is fine since it suits their needs. But I maintain it needs more independant testing, on good-old-not-cloud-server, especially databases (which are not client-side devices). It may very well be that it is positive for that workoad too. Or not. That is all I'm saying.
- notriddle 6y ago
  > But I maintain it needs more independant testing, on good-old-not-cloud-server, especially databases Don't a lot of databases bypass the page cache for their payload data anyhow?
  - jeffbee 6y ago
    Universally. The kernel's page cache is the very last thing that a database operator wants.
    - yuzhao 6y ago
      I'm one of the Google engineers who work on multigenerational LRU. The kernel page cache doesn't know better than databases themselves when it comes to what to cache. All high performance databases do this in user space, and they use AIO with direct IO or the latest io_uring to bypass the kernel page cache. Modern cloud (distributed) file systems do the same, including GFS: https://en.wikipedia.org/wiki/Google_File_System https://en.wikipedia.org/wiki/Google_File_System And speaking of io_uring, check this out to see how much improvement when copying without going through page cache: https://wheybags.com/blog/wcp.html https://wheybags.com/blog/wcp.html
  - jandrewrogers 6y ago
    Yes. Bypassing the kernel cache is a major optimization used by virtually all databases that are serious about prioritizing performance. It won't add anything to the top end of database engine performance. However, there are plenty of databases that do not prioritize performance which could benefit, including most open source ones.
  - ldng 6y ago
    It is not as simple as that : https://www.pgcon.org/events/pgcon_2020/schedule/session/152-asynchronous-io-for-postgresql/ https://www.pgcon.org/events/pgcon_2020/schedule/session/152...