Fallacies of distributed computing

The fallacies are:^[1]

• The network is reliable
• Latency is zero
• Bandwidth is infinite
• The network is secure
• Topology doesn't change
• There is one administrator
• Transport cost is zero
• The network is homogeneous

Although, there are some writings about they are not fallacies anymore... 

iostat vmstat

- vmstat 30
  cpu intensive ?
  memory paging ?
  r, free, si, so

- iostat -x
  avgqr-z
  await
  %util (100%?!)

Run iostat with kilobytes unit, 2 seconds interval with 3 times reports
# iostat -k 2 3

1. https://devwebcl.blogspot.com/2014/05/distinctive-recipes-2nd-ed-1212-1211.html
2. https://www.geeksforgeeks.org/iostat-command-in-linux-with-examples/
3. https://www.techrepublic.com/article/how-to-use-the-linux-iostat-command-to-check-on-your-storage-subsystem/

HTTP 1.0 Performance

HTTP 1.0 had performance issues by slow-start of TCP. The 3-way handshaking was guilty.

https://devwebcl.blogspot.com/2018/09/tcpip-illustrated.html

This was fixed in HTTP 1.1 reusing the connections. Similar to a pool of TCP connections.

2.

• Under HTTP 1.0, connections are not considered persistent unless a keepalive header is included,^[1]
  
  
  ^{-Dhttp.keepAlive=false (it can be configured at java system property)}
  
  
•  In HTTP 1.1, all connections are considered persistent unless declared otherwise.^[2]

Resources:

- https://www.w3.org/Protocols/HTTP/1.0/HTTPPerformance.html
- https://hpbn.co/http1x/
- https://blog.insightdatascience.com/learning-about-the-http-connection-keep-alive-header-7ebe0efa209d
- https://en.wikipedia.org/wiki/HTTP_persistent_connection#HTTP_1.0
- https://en.wikipedia.org/wiki/TCP_congestion_control

HTTP client timeouts

https://docs.spring.io/autorepo/docs/spring-framework/4.1.7.RELEASE/javadoc-api/org/springframework/http/client/HttpComponentsClientHttpRequestFactory.html

        HttpComponentsClientHttpRequestFactory requestFactory =
                new HttpComponentsClientHttpRequestFactory();

        requestFactory.setConnectionRequestTimeout(connectRequestTimeout);
        requestFactory.setConnectTimeout(connectTimeout);
        requestFactory.setReadTimeout(readTimeout);
       


setConnectionRequestTimeout(int connectionRequestTimeout)
Set the timeout in milliseconds used when requesting a connection from the connection manager using the underlying HttpClient.
(del manager!, del http pool, si no tiene conexiones para ofrecer)


setConnectTimeout(int timeout)
Set the connection timeout for the underlying HttpClient.
(conexion con el server)


setReadTimeout(int timeout)
Set the socket read timeout for the underlying HttpClient.
(lectura del response).

Hipérbaton

Del lat. hyperbăton, y este del gr. ὑπερβατόν hyperbatón.

 

1. m. Ret. Alteración del orden que las palabras tienen habitualmente en el discurso, como en por mi mano plantado tengo un huerto.

https://dle.rae.es/?id=KQc0GSw

 

Knuth Quilt

A quick straightforward (and slow) ruby code to create Knuth quilt from Donald Knuth's TAoCP Pre-Fascicle 1a: Bitwise Tricks and Techniques


https://dzone.com/articles/patchwork-quilt-pattern-ruby

 

 

Proof of Concept (POC)

POC is therefore a prototype that is designed to determine feasibility, but does not represent deliverables.

Persistence, Affinity, Sticky session and others

Affinity: this is when we use information from a layer below the application layer to maintain a client request to a single server

Persistence: this is when we use Application layer information to stick a client to a single server

sticky session: a sticky session is a session maintained by persistence

The main advantage of the persistence over affinity is that it’s much more accurate, but sometimes, Persistence is not doable, so we must rely on affinity.

Using persistence, we mean that we’re 100% sure that a user will get redirected to a single server.

Using affinity, we mean that the user may be redirected to the same server…

https://www.haproxy.com/blog/load-balancing-affinity-persistence-sticky-sessions-what-you-need-to-know/

More info:

https://stackoverflow.com/questions/2528935/sending-cookie-with-http-request-in-java

https://stackoverflow.com/questions/4166129/apache-httpclient-4-0-3-how-do-i-set-cookie-with-sessionid-for-post-request

https://docs.oracle.com/cd/E24329_01/web.1211/e21049/sessions.htm#WBAPP323

https://stackoverflow.com/questions/4166129/apache-httpclient-4-0-3-how-do-i-set-cookie-with-sessionid-for-post-request

https://docs.oracle.com/cd/E24329_01/web.1211/e24425/bigip.htm#CLUST574

https://docs.oracle.com/cd/E11035_01/wls100/cluster/load_balancing.html#wp1028843
https://devcentral.f5.com/questions/sticky-session-for-cookiless-clients  (cooki-less) !!!

https://community.oracle.com/thread/3379174

https://serverfault.com/questions/903386/apache-balancing-towards-weblogic-backends-mod-wl-vs-mod-proxy-balancer

ehcache heap dump

After getting a heap dump, we can check several.

select x from net.sf.ehcache.Cache

• net.sf.ehcache.store.cachingtier.CountBasedBackEnd
• net.sf.ehcache.Cache

List Caches:
https://cwiki.apache.org/confluence/display/SHINDIG/EhCache+Memory+Analysis

--> net.sf.ehcache.Cache --> List objects --> with outgoing references --> configuration --> name


JMX MBeans:
https://khushroomistry.wordpress.com/2013/09/24/monitoring-ehcache-spring/

The History of Computer Chess: An AI Perspective

Very impressive talk with chess authorities and computer scientists.

David Levy, Knuth (talking about its paper alpha-beta).