[mapserver-dev] Mapserver causes too many open files error

[Lime, Steve D (MNIT)]

I’m ok with the changes… +1  Anyone else?

From: Tamas Szekeres [mailto:szekerest at gmail.com]
Sent: Sunday, December 10, 2017 12:06 PM
To: Lime, Steve D (MNIT) <steve.lime at state.mn.us>
Cc: mapserver-dev at lists.osgeo.org
Subject: Re: [mapserver-dev] Mapserver causes too many open files error

Hi Steve,

Sorry for the confusion those commits were basically for testing the changes.
I've now uploaded the commits I would prefer to see in mapserver/master:

https://github.com/szekerest/mapserver/commit/def90bfed47abaaba7ec12f49eb218494a39cbdc

https://github.com/szekerest/mapserver/commit/b74fd63f6838f1cf20cee7f1951e8cbac8da443e

With regards to the FastCGI configuration I think that should also work without the USE_THREAD setting which is not affected with the changes. But if we don't set these environment variables, we would get back the original behavior.

Best regards,

Tamas




2017-12-05 21:40 GMT+01:00 Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>:
Seem relatively minor. Couple of questions:


•         Since changes for item 1 would apply more generally, is there any downside for FastCGI or should there be a 3rd state where you have threads AND are using Windows (or is that what you mean by being switchable).

•         Why the symbol change from USE_THREAD to USE_THREAD_NOTSET?

Steve

From: Tamas Szekeres [mailto:szekerest at gmail.com<mailto:szekerest at gmail.com>]
Sent: Friday, December 01, 2017 9:51 AM

To: Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>
Cc: mapserver-dev at lists.osgeo.org<mailto:mapserver-dev at lists.osgeo.org>
Subject: Re: [mapserver-dev] Mapserver causes too many open files error

This change demonstrates what we need in #1

https://github.com/szekerest/mapserver/commit/87cacc6a37e802bc3af16656d45966c05deb4d62

For #2 this is the example:

https://github.com/szekerest/mapserver/commit/e16069972b43f837b47d0f736c2df4d5c0c7a475

Both of them should be switchable which is not yet added to this code example.

Best regards,

Tamas



2017-12-01 15:48 GMT+01:00 Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>:
What does #1 entail? The other change is Windows specific so seems ok – I don’t know what the right value should be of course.

From: Tamas Szekeres [mailto:szekerest at gmail.com<mailto:szekerest at gmail.com>]
Sent: Friday, December 01, 2017 1:53 AM
To: Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>
Cc: mapserver-dev at lists.osgeo.org<mailto:mapserver-dev at lists.osgeo.org>
Subject: Re: [mapserver-dev] Mapserver causes too many open files error

We did some investigation in this regard and the following 2 changes could solve this specific problem on Windows and ASP.NET<http://ASP.NET>.

1. Adding the ability to use a single cache instead of a per-thread cache.

2. Increase the number of open stdio file handle limit for Windows. Default is 512 the upper limit is 2048 accoding to this documentation: https://msdn.microsoft.com/en-us/library/6e3b887c.aspx


These settings should probably be controlled with compile options or environment variables.

Any objections to apply such changes?

Best regards,

Tamas






2017-11-27 16:42 GMT+01:00 Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>:
The former is certainly simpler. How expensive is setting up and clearing out the cache? Probably should look at Thomas’ RFC on the topic.

From: mapserver-dev [mailto:mapserver-dev-bounces at lists.osgeo.org<mailto:mapserver-dev-bounces at lists.osgeo.org>] On Behalf Of Tamas Szekeres
Sent: Sunday, November 26, 2017 2:01 PM
To: mapserver-dev at lists.osgeo.org<mailto:mapserver-dev at lists.osgeo.org>
Subject: [mapserver-dev] Mapserver causes too many open files error

Hi Devs,

We experienced an issue with mapserver 7.x (comparing to 6.x) that it causes too many open file handles in a multi-threaded environment. Actually the process is using the ASP.NET<http://ASP.NET> backend where the web requests are served through the ASP.NET<http://ASP.NET> worker process by using a thread pool, and the process should be considered as a long running process, where msCleanup is not being called regularly.

By looking into the code the issue should probably be dedicated to the global font cache approach implemented in mapserver 7. Since freetype keeps the font files open, we get the number of fonts used in the mapfile multiplied with the thread pool size which may exceed the number of stdio open file handle limit as per https://msdn.microsoft.com/en-us/library/kdfaxaay(v=vs.140).aspx

With the former approach (ie. 6.x) the font cache was implemented in the renderers and the cache cleanup was happening on the renderer cleanup in msFreeOutputFormat/msFreeMap.

Do you have any suggestions about a proper workaround to this?

I might think that we should either bind the font cache to each map objects (like earlier) or use a single common font cache for the entire process. I would probably prefer the first one as soon as we want to clean up every resources what a rendering session allocates.

Thanks,

Tamas





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