I've noticed that when I run a php script on my redis server (simple set / get) that it will load in under 1 ms. If I have two servers, a web server and a redis server, it will take a good 15 ms for the web server to connect, set, and get. Is there a way to make a constant connection between the two servers so I don't need to reconnect every single time the script is called?
It depends on the client library you are using to communicate with redis if it supports/creates a persistent connection or a pool of pre-created connections in order to save initial handshaking for each request.
We have one VM for BizTalk and a separate VM for the SQL backend. We are using Veeam for backups which basically kicks off a snapshot of the VM. When this snapshot is being finalized on the SQL VM, BizTalk services on the application server fail. Usually they restart automatically but sometimes this requires manual intervention to start the services. The error below is logged on the BizTalk server.
Is there any timeout setting or config changes that will allow BizTalk services to stay up during the snapshot process?
An error occurred that requires the BizTalk service to terminate. The most common causes are the following:
1) An unexpected out of memory error.
OR
2) An inability to connect or a loss of connectivity to one of the BizTalk databases.
The service will shutdown and auto-restart in 1 minute. If the problematic database remains unavailable, this cycle will repeat.
Error message: [DBNETLIB][ConnectionRead (recv()).]General network error. Check your network documentation.
Error source:
BizTalk host name: BizTalkServerApplication
Windows service name: BTSSvc$BizTalkServerApplication
We experienced the same situation and error with both BizTalk 2009 and BizTalk 2013, each set up with two App servers and one SQL DB server.
When our VMware does the final step of the Snapshot backup on the Application servers, it freezes the application server for about 10 seconds, preventing it from receiving packets. On SQL Server 2008 and 2012, it by default will send out keep-alive packets to the clients every 30 seconds (30,000 ms). If the SQL server fails to receive a response back from the App server, it will send out 5 retries (default setting) of the keep-alive request 1 second (1,000 ms) apart. If SQL still does not receive the response back, it will terminate the connection, which will cause the BizTalk hosts on the App server to reset, and in our case, when our German-made ERP system sends its EDI documents over to BizTalk during that reset period, the transmission will fail.
We trapped the issue by running NetMon on the DB and App servers, waiting for the next error message. Upon inspection, we see the five SQL keep-alive packets being sent to the App servers 1 second apart, and at the same time there were NO packets at all received on the Application server. At first guess, one might think they were "just dropped network packets", which is rarely the case. We then made the correlation to the timing of the VM Snapshots, and now confirm each time the snapshot finishes each day, the App servers freeze.
As a Short-to-mid-term workaround, we raised the number of retries SQL attempts before declaring a connection dead, (5 by default), by adding the registry value TcpMaxDataRetransmissions and setting it to 30 (thus 30 seconds before SQL declares the client unresponsive). This has masked the problem for now for us, and use at your own discretion.
We are also looking at an Agent-based version of the VM Snapshot, which may alleviate the condition of freezing the server.
Is there any timeout setting or config changes that will allow BizTalk services to stay up during the snapshot process?
Not that I am aware of, however you might want to Google config options in the btsntsvc.exe.config file which is located in your BizTalk installation directory.
All messages that pass through BizTalk are written to the BizTalkMsgBoxDb and its other databases are involved if you are running tracking, BAM etc. The only service that can cache 'stuff' and handle a database outage is the Enterprise Single Sign-On (ESSO) Service. BizTalk therefore needs a persistent connection to the database server to remain 'up', hence why your Host Instance (BizTalkServerApplication) is stopping - it simply wouldn't be able to process messages if the database wasn't there.
I would add that your approach to back-ups probably isn't supported by Microsoft and I would further suggest that you seriously consider whether an approach that takes your database server offline during the backup is viable?
BizTalk has a pretty robust backup solution for its various databases built into the product, and I would recommend that you take a look at using this supported method.
If you do need to take snapshots of the database system - say once a night - you might want to consider stopping the BizTalk Host Instances, performing the snapshot, and then re-starting the Host Instances through some scripted task.
You might also want to consider checking whether there are any hotfixes for your version of BizTalk Server included in a Cumulative Update that might help address your problem.
Imagine situation (this is real situation):
There is a WCF client application on laptop.
Laptop is connected by WiFi to internet.
User is doing some stuff (request reply operations) on his laptop at work connected to WCF service.
Then user's laptop is sleep-down and user go home. At home user wake-up his laptop, connect HSPDA/3G modem (different interface & ip) and want to continue on work in client appliaction. Note that application hasn't been closed.
User (client application) should be authenticated and if it is possible, communication should be encrypted.
What are the best practices?
Create new proxy for each operation? This should be very slow when initializing net.tcp connection with authentication.
Is solution basicHttp connection (+HTTPS) with InstanceContextMode.PerCall? Note that speed and higher payload is problem.
Or the best solution is something like "wrapper(Func<>)", which contains while loop until operation is successfully finished (on fail, new connection is created and function is called again).
Thanks you for suggestions
I've always kept the connection open for as long as the unit of work is necessary. Basically, the connection is only open and available while the application is performing some processing (and those processes require a WCF connection). It may be more overhead to keep reconnecting (and depending on connection speed it may add latency) but it's also more secure when it comes to having a connection to work with (least probability of failure) and I'm generally saving those resources for other purposes.
However, this all depends on what the application does; If the client is dumb and the service is doing all the work it may make sense to keep the connection as every function executes a method on the service. Though with that comes some failure checking and re-establishing should the connection be unexpectedly severed.
Also, netTcp is going to be a lot faster than wsHttp. And I personally haven't see a lot of latency on establishing a netTcp connection (though I don't know what kind of authentication you're doing [mine has generally implemented windows authentication])
I don't think I was clear. What I meant was How to set a callback("server to client") in a different connection from a "client to server" connection using WCF ?
I always saw callbacks examples using just one DuplexChannelFactory. This implies using only one TCP connection to make client to server calls and receive server to client callbacks.
This question came to me after I read this this topic:
Seeking WCF Duplex "TwoWay" Subscribe+Callback Example
I the top answer, Ian Ringrose said:
Some rules I found to help avoid deadlocks. (Look at my WCF questions to see the pain I had!)
The sever must never call out to a client on the same connection as a call from the same client is in process on.
And/or
The client must never call back to the server on the same connection as is used for the “callbacks” while processing a call-back.
And I was wondering how to implement it using WCF.
This CodeProject on Robust Interapplication Communications using Double-Simplex WCF answers exactly your question:
What I decided to do was run two separate WCF connections (double simplex). Each application would run a WCF Host for incoming messages and each application would run a WCF Client for outgoing messages. This is a pretty robust solution and will not be broken by stopping and starting the applications. The WCF Client simply re-establishes the connection if needed.
The way it is solved meets the requirements you have extracted from the Ian Ringrose answer.
The setup is as follows:
A C++ client connects via OLEDB/SQL Native Client to a SQL Server 2005 database located on another machine. The server is setup with mirroring (automatic failover) with a synchronized server located on yet another server and a witness server on another server.
Occassionally (once every couple of days), our application seizes up in that it appears to attempt to establish a database connection to the database and rather than simply failing and OLEDB throwing a database connection failure it just gets "stuck" (we have a timeout for the connection but it's never timing out). 24 to 36 hours later we'll get an error:
TCP Provider: An existing connection was forcibly closed by the remote host.
And things will continue you on with lots of these errors and our app will eventually need to be restarted. We can't really figure out what condition could be causing this behavior and what we can do about it?
In preliminary research, I've seen some related problems that were solved by setting the Connection Lifetime connection string property to something non-zero.
Does anyone have any thoughts on what might be going on here?