[Buildbot-devel] big custom logs horking the status web server?

[Brian Warner]

> This has been working fine for a while but I just enabled every  
> warning I could and now the webserver status page is choking when I  
> click on the "warnings" log.  The error page generated by the  
> webserver is at the end of this email and it's pretty long.

Ah, got it. When you use addCompleteLog(), you get a single huge chunk in the
file that gets saved to disk. This file is saved as a series of netstrings,
and Twisted's standard netstring-parsing class happens to have a built-in
limit on how large of a string it will accept. The default is 100k, so any
one-chunk log that is bigger than this will blow up when you try to view it.
The error message is confused by the fact that I'm using NetstringReceiver in
a slightly weird way (the protocol responds to the "malformed" oversized
netstring by trying to hang up, but I didn't give it a .transport attribute
to do that with).

The quick solution is to bump up this limitation:

--- orig/buildbot/status/builder.py
+++ mod/buildbot/status/builder.py
@@ -45,6 +45,7 @@
 ChunkTypes = ["stdout", "stderr", "header"]
 
 class LogFileScanner(basic.NetstringReceiver):
+    MAX_LENGTH=10*1000*1000
     def __init__(self, chunk_cb, channels=[]):
         self.chunk_cb = chunk_cb
         self.channels = channels


The better solution (which I'll put into the next revision) is to change
addCompleteLog to break up the log text into smaller chunks (probably 10k,
because that matches LogFile.chunkSize, used by the normal streaming
Step.addLog). This also improves read-time delivery of the LogFile contents,
because it only has to buffer one chunk in memory at a time, and smaller
chunks mean less RAM requirements.

I'll send out a patch with the smaller-chunks change when it's done, so you
can apply it to 0.6.6 instead of jumping to the (unstable) CVS tree quite
yet.

cheers,
 -Brian