minFileSizeForComp is not working for dynamic compression in IIS10

Question

minFileSizeForComp is not working for dynamic compression in IIS10

Kaumudi Rawat 0

I am trying to change the minFileSizeForComp from the default of 2700 bytes to 860 bytes. But it is not working for dynamic compression gzip/deflate.

I am able to compress API response <2700 bytes as well. IIS httpcompression "minFileSizeForComp" property does not seems to be working for dynamic compression.

Is there any way to make it work at server/site level for IIS10 . Appreciate the help!

Lex Li 6,037 Reputation points

2024-01-27T08:47:48.6666667+00:00

Have you checked out https://stackoverflow.com/questions/8250295/does-minfilesizeforcomp-httpcompression-attribute-even-work ?
Sam Wu-MSFT 7,561 Reputation points Microsoft External Staff

2024-01-29T08:54:10.31+00:00

@Kaumudi Rawat It will be difficult to understand what is happening, you can try use failed request tracking to view detailed information, this will generate detail log file, which will help you to identify the problem.
Kaumudi Rawat 0 Reputation points

2024-01-30T04:46:02.1633333+00:00

@Lex Li , thank you for the response.
I already visited this article and it talks about solutions when IIS is not respecting the minFileSizeForComp settings for static compression due to dynamic compression is also enabled for that mimetype.
It also says "Another note is that this setting will be ignored for the dynamic compression as a by-design behavior."
Seems like we cannot set minimum size for dynamic compression. It will compress all API responses regardless of the size. Could you please confirm.
Thank you.
Kaumudi Rawat 0 Reputation points

2024-01-30T04:52:46.25+00:00

Hi Sam Wu-MSFT, thank you for the response, I have already tried "failed request tracking" feature but as in my case IIS is compressing dynamic API responses of all size and in the log file what I am getting is that dynamic compression succeeded. I need to know why it is getting succeeded even for API responses<2700 bytes (minFileSizeForComp default size). I guess this feature can help in cases where compression does not succeed and tells us the reason. But here I need to know the reason of success not failure.
Seems like we cannot set minimum size for dynamic compression. It will compress all API responses regardless of the size.

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Lex Li 6,037 Reputation points

2024-01-27T08:47:48.6666667+00:00

Have you checked out https://stackoverflow.com/questions/8250295/does-minfilesizeforcomp-httpcompression-attribute-even-work ?
Sam Wu-MSFT 7,561 Reputation points Microsoft External Staff

2024-01-29T08:54:10.31+00:00

@Kaumudi Rawat It will be difficult to understand what is happening, you can try use failed request tracking to view detailed information, this will generate detail log file, which will help you to identify the problem.
Kaumudi Rawat 0 Reputation points

2024-01-30T04:46:02.1633333+00:00

@Lex Li , thank you for the response.
I already visited this article and it talks about solutions when IIS is not respecting the minFileSizeForComp settings for static compression due to dynamic compression is also enabled for that mimetype.
It also says "Another note is that this setting will be ignored for the dynamic compression as a by-design behavior."
Seems like we cannot set minimum size for dynamic compression. It will compress all API responses regardless of the size. Could you please confirm.
Thank you.
Kaumudi Rawat 0 Reputation points

2024-01-30T04:52:46.25+00:00

Hi Sam Wu-MSFT, thank you for the response, I have already tried "failed request tracking" feature but as in my case IIS is compressing dynamic API responses of all size and in the log file what I am getting is that dynamic compression succeeded. I need to know why it is getting succeeded even for API responses<2700 bytes (minFileSizeForComp default size). I guess this feature can help in cases where compression does not succeed and tells us the reason. But here I need to know the reason of success not failure.
Seems like we cannot set minimum size for dynamic compression. It will compress all API responses regardless of the size.

Answer 1

Sam Wu-MSFT 7,561 Microsoft External Staff

@Kaumudi Rawat An HTTP client must initiate communication for compressed content by sending the appropriate HTTP Accept-encoding header. If a client is not capable of HTTP compression, it will not pass that header and IIS will always return uncompressed content, so please check how good your Accept-Encoding is working on the site.

To check Accept-Encoding in action go to Inspect Element -> Network check the request header for Accept-Encoding

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Kaumudi Rawat 0 Reputation points

2024-01-31T11:48:24.2733333+00:00

Hi @Sam Wu-MSFT thank you for your response. I am sending "Accept-Encoding" request header as gzip/deflate. It is working fine for both compressions when configured at server (applicationHost.config) level. The problem is, I am not able to set the minimum response size for dynamic compression for APIs. All API response regardless of the size are getting compressed. "minFileSizeForComp" does not seems to be working for dynamic compression. Is there any way to set the minimum response size for dynamic compression in IIS 10? Really appreciate your help here. thanks
Sam Wu-MSFT 7,561 Reputation points Microsoft External Staff

2024-02-02T10:01:53.4833333+00:00

@Kaumudi Rawat It is difficult to reproduce your problem based on your description, I suggest you open a case via: https://support.microsoft.com.
Kaumudi Rawat 0 Reputation points

2024-02-02T10:08:33.52+00:00

Hi Sam Wu-MSFT, thank you for the help!

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minFileSizeForComp is not working for dynamic compression in IIS10

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