A VPS Server I had just wasn't working right, code that I migrated there just wasn't working.  For example, it kept telling me the connection to the database was unsuccessful, halfway through iterating through results it already had.

Then I realized it wasn't my code.  I checked my /proc/user_beancounters and found this:

  cat /proc/user_beancounters
Version: 2.5
       uid  resource           held    maxheld    barrier      limit    failcnt
     2000:  kmemsize        2499074    3453079  268435456  268435456       2985
            lockedpages           0          8     999999     999999          0
            privvmpages       43361      87480    1024000    1024000          0
            shmpages            671       1647      65536      65536          0
            dummy                 0          0          0          0          0
            numproc              32         48     999999     999999          0
            physpages         10119      24142          0 2147483647          0
            vmguarpages           0          0    1024000    1024000          0
            oomguarpages      10119      24142       6144 2147483647          0
            numtcpsock            6         24    7999992    7999992          0
            numflock              8         12     999999     999999          0
            numpty                1          1     500000     500000          0
            numsiginfo            0          6     999999     999999          0
            tcpsndbuf         69316     380120  235713536  235713536          0
            tcprcvbuf         98304    1527656  235713536  235713536          0
            othersockbuf       8944     175584  235713536  235713536          0
            dgramrcvbuf           0       8380  235713536  235713536          0
            numothersock         12         32    7999992    7999992          0
            dcachesize       220365     274667 2147483646 2147483646          0
            numfile            1116       2025   23999976   23999976          0
            dummy                 0          0          0          0          0
            dummy                 0          0          0          0          0
            dummy                 0          0          0          0          0
            numiptent             5          5        128        128          0

Notice the "failcnt" for "kmemsize" is 2985.  The value was too low, in this quote it had already been corrected and after that my PHP scripts were working fine.

When things don't make sense and aren't working properly, check your "beancounters" to make sure nothing is failing.

Also remember not to instantly blame your VPS Provider, lots of times people have these problems when running intensive scripts, applications, CPanel/Plesk and it's because your plan does not have enough RAM etc...

This should be something every admin/owner of a VPS checks routinely for inexplicable problems/timeouts with your applications in a VPS Server.

OpenVZ technology is the best for performance, but the settings must be just right to avoid problems, and you must make sure you have a plan that meets your needs.  There's no such thing as swapping, if you exceed your limits, connections drop, application/database calls fail without explanation.

So just remember to pick a VPS/Virtual Private Server plan that meets you needs and monitor the beancounters for any signs of failures.