You are viewing a plain text version of this content. The canonical link for it is here.
Posted to users@solr.apache.org by Karl Stoney <Ka...@autotrader.co.uk.INVALID> on 2021/03/13 18:36:03 UTC

documentCache vs IO Cache?

Hi,
Apologies if this is a silly question, I just can't find anything explaining the benefits online.

Would anyone be able to tell me why you would use a documentCache, if you have sufficient RAM on your machine that the OS disk cache is effectively caching all the documents anyway?

Thanks!
Unless expressly stated otherwise in this email, this e-mail is sent on behalf of Auto Trader Limited Registered Office: 1 Tony Wilson Place, Manchester, Lancashire, M15 4FN (Registered in England No. 03909628). Auto Trader Limited is part of the Auto Trader Group Plc group. This email and any files transmitted with it are confidential and may be legally privileged, and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the sender. This email message has been swept for the presence of computer viruses.

Re: documentCache vs IO Cache?

Posted by Karl Stoney <Ka...@autotrader.co.uk.INVALID>.
OK this makes sense, thanks for the reply Shawn.

On 13/03/2021, 21:34, "Shawn Heisey" <ap...@elyograg.org> wrote:

    On 3/13/2021 11:36 AM, Karl Stoney wrote:
    > Apologies if this is a silly question, I just can't find anything explaining the benefits online.
    >
    > Would anyone be able to tell me why you would use a documentCache, if you have sufficient RAM on your machine that the OS disk cache is effectively caching all the documents anyway?

    I'm pretty sure that the document cache stores uncompressed data.  With
    the disk cache, the decompression step would be required, using CPU
    resources and taking a little bit of time.  Reading from the document
    cache would be faster and not hit the CPU as hard.

    Since I think version 4.1, Solr (Lucene, really) writes stored fields in
    compressed format.

    Thanks,
    Shawn

Unless expressly stated otherwise in this email, this e-mail is sent on behalf of Auto Trader Limited Registered Office: 1 Tony Wilson Place, Manchester, Lancashire, M15 4FN (Registered in England No. 03909628). Auto Trader Limited is part of the Auto Trader Group Plc group. This email and any files transmitted with it are confidential and may be legally privileged, and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the sender. This email message has been swept for the presence of computer viruses.

Re: documentCache vs IO Cache?

Posted by Shawn Heisey <ap...@elyograg.org>.
On 3/13/2021 11:36 AM, Karl Stoney wrote:
> Apologies if this is a silly question, I just can't find anything explaining the benefits online.
> 
> Would anyone be able to tell me why you would use a documentCache, if you have sufficient RAM on your machine that the OS disk cache is effectively caching all the documents anyway?

I'm pretty sure that the document cache stores uncompressed data.  With 
the disk cache, the decompression step would be required, using CPU 
resources and taking a little bit of time.  Reading from the document 
cache would be faster and not hit the CPU as hard.

Since I think version 4.1, Solr (Lucene, really) writes stored fields in 
compressed format.

Thanks,
Shawn