[next] [previous] [contents] [full-page]18.1 - Simple File Request Turn-Around
18.2 - Scripting
18.3 - SSL
18.4 - Suggestions
The server has a single-process, multi-threaded, asynchronous I/O design. On a single-processor system this is the most efficient approach. On a multi-processor system it is limited by the single process context (with scripts executing within their own context). For I/O constrained processing (the most common in general Web environments) the AST-driven approach is quite efficient.
The server has been tested with up to 60 concurrent requests originating from 6 different systems and continues to provide an even distribution of data flow to each client (albeit more slowly :^) The author has also observed sites where traffic levels frequently reach 50 to 100 concurrent requests both for standard and proxy serving.
The test system was a lightly-loaded AlphaServer 2100 4/275, VMS v7.2-1 and DEC TCP/IP 5.1. No Keep-Alive: functionality was employed so each request required a complete TCP/IP connection and disposal. DNS (name resolution) and access logging were disabled. The server and test-bench utility were located on separate systems with 100 Mbps FDDI network interconnection.
As of v7.1 the performance data is collected using the "ApacheBench" utility (see 20.4 - ApacheBench). Previous comparisons were performed using the WASD WWWRKOUT utility but it was felt the use of a more common tool would be the prefered option. DCL procedures with sets of ApacheBench calls are used to benchmark requests. These procedures and the generated output from benchmark runs (collected via $@procedure/OUTPUT=filename) are available in the HT_ROOT:[EXERCISE] directory.
These results are indicative only!
On a clustered, multi-user system too many things vary slightly all the time. Hence the batching of accesses, interleaved between servers, attempting provide a representative result.
Until v5.3 a direct comparison of performance between OSU and WASd had not been made (even to satisfy the author's own occasional curiosity). After a number of users with experience in both environments commented ... WASD seemed faster, was it? ... it was decided to make and provide comparisons using the same metrics used on WASD for some time.
Every endeavour has been made to ensure the comparison is as equitable as possible (e.g. each server executes at the same process priority, has a suitable cache enabled, runs on the same machine in the same relatively quiescent environment. Each test run was interleaved between each server to try and distribute any environment variations. Tests showing a port 7080 were to WASD, port 7777 to the OSU server, and port 8888 to Apache. All servers were configured "out-of-the-box", minimal changes (generally just path mappings), WASD executing via the FREEWARE_DEMO.COM procedure.
Of course performance is just one of a number of considerations in any software environment (otherwise we wouldn't be using VMS now would we? ;^) No specific conclusions are promoted by the author. Readers may draw their own from the results recorded below.
For this document the results were derived using the WASD v7.2, CSWS
V1.1 (VMS Apache 1.3.14), and OSU 3.9a servers.
18.1 - Simple File Request Turn-Around
A series of tests using batches of accesses. The first test returned an empty file measuring response and file access time, without any actual transfer. The second requested a file of 64K characters, testing performance with a more realistic load. All were done using one and ten concurrent requests. Note that the Apache measurement is "out-of-the-box" - the author could find no hint of a file cache, let-alone how to enable/disable one.
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Result files:
With both WASD cached and non-cached throughput actually improves at ten concurrent requests (undoubtably due to the latency of the serial TCP/IP connection/disconnection in one-by-one, compared to several happening concurrently).
Note that the response and transfer benefits decline noticably with file size (transfer time). The difference between cached and non-cached with the zero file size (no actual data transfer involved) gives some indication of the raw difference in response latency, some 300-400% improvement. This is a fairly crude analysis, but does give some indication of cache efficiencies.
Just one other indicative metric of the two servers, CPU time consumed during the file measurement runs. The value for Apache was not measured as it would be distributed over an indeterminate number of child processess.
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Under similar conditions results indicate a potential transfer rate well in excess of 1 Mbyte per second. This serves to demonstrate that server architecture should not be the limiting factor in file throughput.
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Result files:
Significantly, there were no dramatic drops in transfer rate between
one and ten concurrent requests! The results for Apache indicate one occasion
where a collection of child processes performs very well (with assistance from
generous VCC_... cache settings).
File Record Format
The server can handle STREAM, STREAM_LF, STREAM_CR, FIXED and UNDEFINED record formats very much more efficiently than VARIABLE or VFC files.
With STREAM, FIXED and UNDEFINED files the assumption is that HTTP carriage-control is within the file itself (i.e. at least the newline (LF), all that is required required by browsers), and does not require additional processing. With VARIABLE record files the carriage-control is implied and therefore each record requires additional processing by the server to supply it. Even with variable record files having multiple records buffered by the HTTPd before writing them collectively to the network improving efficiency, stream and binary file reads are by Virtual Block and are written to the network immediately making the transfer of these very efficient indeed!
So significant is this efficiency improvement a module exists to
automatically convert VARIABLE record files to STREAM-LF when detected by the
file transfer module. This is disabled by default but the user is strongly
encouraged to enable it and to ensure that stream format files are provided
to the server by other hypertext generating and processing utilitites.
18.2 - Scripting
Persistant-subprocesses are probably the most efficient solution for child-process scripting under VMS. See "Scripting Environment" document. The I/O still needs to be on-served to the client by the server.
A simple performance evaluation shows the relative merits of the four WASD scripting environments available, plus a comparison with OSU and Apache. HT_ROOT:[SRC.CGIPLUS]CGIPLUSTEST.C, which executes in both standard CGI and CGIplus environments, and an ISAPI example DLL, HT_ROOT:[SRC.CGIPLUS]ISAPIEXAMPLE.C, which provides equivalent output. A series of accesses were made. The first test returned only the HTTP header, evaluating raw request turn-around time. The second test requested a body of 64K characters, again testing performance with a more realistic load.
DECnet-based scripting was tested using essentially the same environment as subprocess-based CGI, assessing the performance of the same script being executed using DECnet to manage the processes. Three separate environments have been evaluated, WASD-DECnet-CGI, WASD-OSU-emulation and OSU. The OSU script used the WASD CGISYM.C utility to generate the required CGI symbols (also see WASD/OSU Comparison). DECnet-Plus T5.0.3 was in use.
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Result files:
Although these results are indicative only, they do show CGIplus and ISAPI to have a potential for improvement over standard CGI from a factor of 5 (500%) up to factors in excess of 10 (1000%) - a not inconsiderable improvement. Of course this test generates the output stream very simply and efficiently and so excludes any actual processing time that may be required by a "real" application. If the script/application has a large activation time the reduction in response latency could be even more significant (e.g. Perl scripts and RDMS access languages).
CGIplus under V7.2 has seen a dramatic increase in
throughput over previous version benchmarks ... in excess of a factor
of 2 (100%)! This is entirely due to the new "struct" mode available.
See the Scripting Overview for further detail.
DECnet Observations
This section comments on non-persistant scripts (i.e. those that must run-up and run-down with each request - general CGI behaviour). Although not shown here measurements of connection reuse show significant benefits in reduced response times, consistency of response times and overall throughput, showing a difference of some 200% over non-reuse (similar improvements were reported with the OSU 3.3a server).
With ten simultaneous and back-to-back scripts and no connection reuse many more network processes are generated than just ten. This is due to the NETSERVER maintenance tasks such as log creation and purging, activating and deactivating the task, etc., adding latency into this script environment. The throughput was generally still lower than with subprocess-based scripting.
While earlier versions cautioned on the use of DECnet-based scripting this
has been relaxed somewhat through connection reuse.
WASD/OSU Comparison
A direct comparison of CGI performance between WASD and OSU scripting is
biased in favour of WASD, as OSU scripting is based on it's own protocol with
CGI behaviour layered-in above scripts that require it. Therefore a non-CGI
comparison was devised. The script,
HT_ROOT:[SCRIPT]FACE2FACE.COM,
is designed to favour neither environment, merely return the plain-text string
"Hello! " as quickly as possible.
$! OSU and WASD scripting face-to-face in a script that favours neither unduly
$ if f$type(WWWEXEC_RUNDOWN_STRING) .nes. ""
$ then
$ write net_link "<DNETTEXT>"
$ write net_link "200 Success"
$ write net_link "Hello!"
$ write net_link "</DNETTEXT>"
$ else
$ write sys$output "Content-Type: text/plain"
$ write sys$output ""
$ write sys$output "Hello!"
$ endif
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Result files are the same as for scripting metrics above.
18.3 - SSL
At this time there are no definitive measurements of SSL performance (see
14 - Secure Sockets Layer). One might expect that because of the
CPU-intensive cryptography employed in SSL requests that performance,
particularly where concurrent requests are in progress, would be significantly
lower. In practice SSL seems to provide more-than-acceptable responsiveness.
18.4 - Suggestions
Here are some suggestions for improving the performance of the server, listed in approximate order of significance. Note that these will have proportionally less impact on an otherwise heavily loaded system.
TCPIP> SHOW INTERFACE
Packets
Interface IP_Addr Network mask Receive Send MTU
SE0 203.127.158.3 255.255.255.0 376960 704345 1500
LO0 127.0.0.1 255.0.0.0 306 306 0
In this example the MTU of the ethernet interface is 1500 (bytes). Set the [BufferSizeNetWrite] configuration directive to be some multiple of this. In the case of 1500, say 3000, 4500 or 6000. Also set the [BufferSizeDclOutput] to the same value. Rationale: always use completely filled network packets when transmitting data.