SAP HANA CDS ( Core Data Services )Posted: February 24, 2014 Filed under: HANA, SAP, SAP ABAP | Tags: ABAP, HANA, SAP Leave a comment
With SAP HANA platform, there has been a major shift in the way database is looked at. Traditionally, ABAP developers brought most of the data back to application server and manipulated based forming the core logic of the application.With HANA, the emphasis has been to do more in the databse ( akka code pushdown ).
However, there are some major drawbacks:
– It relies on development in two areas : HANA views / procedures which are then consumed in ABAP.
– Two separate mechanisms for ALM with ABAP and HANA transports.
With SAP NW 7.4 SP5, ABAP open SQL has been enhanced and views can be created using DDL. This is known as CDS ( Core Data Services ) .
Looking at an example: Create a basic view.
And the view can be consumed in ABAP – Need to add @ annotation .
These can be extended so that if DDIC additions are made, the view gets them automatically.
And the views can be made more complex.
and even more complex.
This to me looks like a step in the right direction as:
– it’s open SQL and hence is dB agnostic. Hence, it can be supported for other vendors databases in future.
– No separate development done in HANA reducing complexity of application development
ABAP SP5 on HANA is outPosted: February 20, 2014 Filed under: HANA, SAP Leave a comment
Cloud Appliiance Library has been updated with SP5. This is a big release as it has lot of “code push down” features.
Performance Worklist Tool: The SQL Performance Worklist (Transaction: SWLT) allows you to correlate SQL runtime data with ABAP code analysis to plan optimizations using results from the new SQLMonitor and CodeInspector.
CDS Viewbuilding: CDS Viewbuilding is drastically improving the existing viewbuilding mechanisms in ABAP.
Extended OpenSQL: Open SQL has been enhanced with new features, especially a lot of limitations have been removed, the JOIN functionality has been enhances as have been arithmetical and string expressions.
ABAP managed Database Procedures (AMDP): AMDPs enables you to create database procedures directly in ABAP using e.g. SQL Script and to seamlessly integrate it in modern ABAP development. An AMDP can be implemented using an ABAP method.
And then there are additions to ABAP.
– MOVE-CORRESPONDING for Internal Tables : No longer RTTI required for such activities.
and some more:
Expressions and Functions
Open SQL additions
Two more enhancements with the solution from CAL ( Cloud Appliance Library ) :
– Front End provided , installation of eclipse and HANA studio no longer mandatory e.g. if you have a mac.
– BW is present in the same system.
SAP ABAP HANA AWS IssuesPosted: February 11, 2014 Filed under: HANA, SAP Leave a comment
Many a times the HANA instance doesn’t work even though CAL shows green status. We can try just restarting or use the below steps.
- Connect to the instance via putty
- On the command prompt please execute cat /etc/hosts
and check if the ip address of the instance is correctly mapped to the hostname
- Switch user via command: su – a4hadm
- Execute the commands:
ABAP status: sapcontrol -nr 00 -function GetProcessList
HANA status: sapcontrol -nr 02 -function GetProcessList
- If everything is green you have a connectivity problem this means SAP GUI can’t connect via
your VPN connection to the instance.
- If either of the services shows gray or not green, you have to option to restart the complete
instance via the CAL console or you refer to the description in paragraph 8.2
of the document http://scn.sap.com/docs/DOC-45725
which describes how you manually start and stop the services.
SAP ABAP HANA AdditionsPosted: February 11, 2014 Filed under: HANA, SAP Leave a comment
HANA SQLScript Reference :
Click to access SAP_HANA_SQL_Script_Reference_en.pdf
SHINE Ref :
Click to access SAP_HANA_Interactive_Education_SHINE_en.pdf
Code push down has been the key with HANA but with AMDP ( ABAP Managed Database Procedures ) and CDS ( Core Data Services ), the extra effort of creating objects in HANA as well as ABAP doesn’t need to be done anymore.
AMDP :ABAP Managed Database Procedures are a new feature in AS ABAP allowing developers to write database procedures directly in ABAP. You can think of a Database Procedure as a function stored and executed in the database. The implementation language varies from one database system to another. In SAP HANA it is SQL Script. Using AMDP allows developers to create and execute those database procedures in the ABAP environment using ABAP methods and ABAP data types.AMDPs are introduced to easily enable you to get the best out of ABAP for HANA following the “code push-down” paradigm first introduced with SAP NetWeaver AS ABAP 7.4 .
Creating an AMDP is as easy as it can get in ABAP. You can simply implement SQLScript in an ABAP method:
METHOD <meth> BY DATABASE PROCEDURE
< Insert SQLScript code here >
– Every class with AMDP must use interface IF_AMDP_MARKER_HDB.
AMDPs are visible through SE80 but can’t be edited from there.
ABAP Object Services: Some useful additionsPosted: February 9, 2014 Filed under: HANA, SAP, SAP ABAP | Tags: HANA, SAP, SAP ABAP Leave a comment
From my SCN blog : http://scn.sap.com/community/abap/blog/2014/02/09/abap-object-services-some-useful-additions-to-persistent-and-transient-objects
All modern programming language environments have some kind of ORM ( Object Relationship Mechanism ) mechanism. It allows persistence to be represented as programming language objects. In ABAP object services, we have persistent objects to hold data which we’ll save to database and transient objects to hold data in ABAP memory temporarily.
This blog summarizes my experiences in the additions I had to make while using object services in ABAP.
– In the points 1 and 2, I describe two features I wasn’t aware of but found them based on requirements.
– The last three examples under point 3 are enhanced methods I had to create using RTTI as they’re not created “out of box” by persistent generator mechanism – they’re not strictly persistence but I found myself wishing them with my persistent objects.
Just to recap about persistent objects, we can get a persistence reference and set values later. So in the below example, lo_flight is a persistent object and we can update price.
Below are the additions I had to make to get object services working efficiently in my own experience.
- Adding extra ( non-persistent ) fields to a persistent object : What if we need an attribute on the persistent objects not part of the underlying database table. These can be added as an attribute .
And then will show up as an attribute in the “Persistence Representant” view. As seen below, the attribute gets added .
The field gets added as a normal attribute to the class and can be removed (attributes coming from the table can’t be removed as they’re greyed out ).
As an example, I had to identify if a peristent object has been changed and I added an extra field ‘update’ for this purpose.
and then tie this attribute with the event IF_OS_STATE~CHANGED to indicate when the object has been modified.
This can be handy if a transient object is converted into a persistent object . e.g. A screen’s PBO gets the transient object and the PAI can check if the object has been modified to trigger the conversion from a transient object to a persistent object.
2. Transient objects in place of ABAP memory: Using transient objects for structures to store memory within a session (as a replacement for ABAP Memory). Many a times, to transfer data with in a session, we export data into ABAP memory and then import it back again. This is fine but this can be difficult to debug in case the export / import locations are not well documented ( imagine data being exported to ABAP memory from an enhancement deep down in a stack and then trying to debug through to find why it’s not set).
A substitute can be to create transient objects from structures.
And we can create a business key which can hold distinct values.
Looking at the method definitions.
We can create a transient object.
and then retrieve the values.
However, if the CREATE_TRANSIENT and GET_TRANSIENT are not in the same stack , this will fail . e.g. if the GET_TRANSIENT was called in a V1/V2 update process whereas the CREATE_TRANSIENT was in the main process, GET_TRANSIENT will fail.The below diagram represents it diagrammatically.
We still need to use SAP memory but at-least we can replace ABAP memory export / import calls by TRANSIENT objects.
3. Enhanced methods in persistence classes: The last three enhancements are based on addition of new methods to persistent classes. Like regular classes, methods can be added to them and are retained even with regeneration due to data dictionary modifications.
a) “Persist” transient objects: Converting transient objects into persistent objects: In point 1, if the object was modified, I was converting the transient object into a persistent one.
It is handy to be able to save a transient object into a persistent one. E.g. duing PBO of a screen, a transient object was created to read attributes and if attributes are modified, the save can be triggered by converting transient objects into persistent objects.
The below method can be called over the attributes we’re interested in persisting .
data: ls_method type seocmpname,
* ls_class type seoclsname,
lt_params type abap_parmbind_tab,
ls_param type abap_parmbind,
dref type ref to data,
lo_excep type ref to cx_sy_dyn_call_error, “#EC NEEDED
ls_par type abap_parmname.
field-symbols: <fs_attr_value> type any.
* To call the dynamic set_* methods, we need to populate kind, name and ref to actual value
* Create the dynamic method name : SET_<attribute>
concatenate ‘set_’ im_attr into ls_method.
translate ls_method to upper case. “#EC TRANSLANG
* Populate ref to data value
create data dref type (im_data_element).
assign dref->* to <fs_attr_value> .
<fs_attr_value> = im_attr_val .
ls_param-value = dref.
*We’re only setting values => param type is exporting
ls_param-kind = cl_abap_objectdescr=>exporting.
* Create the dynamic param name to be passed
concatenate ‘i_’ im_attr into ls_par.
translate ls_par to upper case.
ls_param-name = ls_par.
insert ls_param into table lt_params .
* Call the dynamic method
call method me->(ls_method)
catch cx_sy_dyn_call_error into lo_excep.
raise exception type zcx_test_update
exporting textid = zcx_test_update=>dynamic_method_call_error .
b) Convert persistent objects to structure : Sometimes we need to get the structure of persistent objects as there are some operations that can’t be done otherwise e.g. value comparison of all fields. It’s required to convert the peristent objects into structures.
DATA: lrf_structdescr TYPE REF TO cl_abap_structdescr,
lv_method_name TYPE seomtdname,
ls_component TYPE abap_compdescr.
FIELD-SYMBOLS: <fs_component> TYPE ANY.
* Request description of transferred structure
lrf_structdescr ?= cl_abap_typedescr=>describe_by_data( ch_struct ).
* Loop via all components of the transferred structure
LOOP AT lrf_structdescr->components INTO ls_component.
* Set the field symbol to the component of the transferred
ASSIGN COMPONENT ls_component-name OF STRUCTURE ch_surgery
* Compose the name of the GET method
CONCATENATE ‘GET_’ ls_component-name INTO lv_method_name.
* Determine the value of the attribute via a dynamic call of
* the GET method and write the value to the structure
CALL METHOD me->(lv_method_name)
result = <fs_component>.
c) Convert structures to persistent objects: And we sometimes need to convert the structure back to a persistent object.
RT_TEST is a reference to the persistence object.
DATA: lo_rtti_struc TYPE REF TO cl_abap_structdescr,
lt_field_list TYPE ddfields,
attr TYPE string,
attr1 TYPE string,
attr_val TYPE string.
FIELD-SYMBOLS: <fs_field> TYPE dfies,
<fs_attr_val> TYPE ANY,
<fs_attr_val1> TYPE ANY.
lo_rtti_struc ?= cl_abap_structdescr=>describe_by_name( struct_name ).
lt_field_list = lo_rtti_struc->get_ddic_field_list( ).
LOOP AT lt_field_list ASSIGNING <fs_field>.
CONCATENATE ‘me->’ <fs_field>-fieldname INTO attr .
TRANSLATE attr TO UPPER CASE.
ASSIGN (attr) TO <fs_attr_val>.
IF sy-subrc = 0.
attr_val = <fs_attr_val>.
attr = <fs_field>-fieldname.
CONCATENATE ‘RT_TEST-‘ <fs_field>-fieldname INTO attr1 .
ASSIGN (attr1) TO <fs_attr_val1>.
<fs_attr_val1> = attr_val.
SAP HANA with ABAP InstallationPosted: February 3, 2014 Filed under: SAP, Software | Tags: ABAP, HANA, SAP Leave a comment
These steps suffice for installation.
1. Order the appliance from SAP Cloud Appliance Library.
2. Update AWS details and start the instance.
3. Download Hana Studio, SAPGUI and ABAP ( for Eclipse ) tools.
4. Install the IDEs – don’t install in Program Files. I had issues in getting the ABAP add-ons to show up . Installed in a separate folder and it worked fine.
5. Install licenses for HANA and SAP ABAP systems from SAP’s mini license site: https://websmp230.sap-ag.de/sap(bD1lbiZjPTAwMQ==)/bc/bsp/spn/minisap/minisap.htm
5. Takes around 40 minutes to start the first time around!
The system can be started / stopped from AWS as well but I’ve noticed that while starting the AWS console shows it’s working muche earlier. I prefer Cloud Appliance Library URL – https://caltdc.hana.ondemand.com/
Reference Links :
DEV GUIDE :
Click to access SAP_HANA_Interactive_Education_SHINE_en.pdf
End to End Scenario :
Developer id : DEVELOPER with master password during installation.
SAP HANA : SAP Landing Page
iOS memory managementPosted: February 2, 2014 Filed under: iOS/ ObjectiveC, Mobile Leave a comment
– All objects have a property retaincount.
– copy, new, alloc and retain increase retain count by 1.
– release decreases retain count.
-autorelease decreases retaincount when the current run loop gets finished.
– Can create your own autorelease pools and drain them to reclaim memory.
Zones: Without zones small and large objects will be created together causing fragmentation. With zones, system creates two different zones – separate ones for different sizes of objects.
– Objects returned by Cocoa are normally autoreleased.
-in dealloc : [aProperty release]
or [self.property = nil]
bugs : app crash: something has been released or auto released and is being accessed
memory leak : memory was allocated but hasn’t been reclaimed even though not required
With ARC : Memory gets deallocated when all strong variables pointing to it are deallocated.
Strong, weak and unsafe_retained:
Strong : Valid till runtime and automatically released. Default for all local variables.
Weak : Zeroes ( sets to null ) the weak reference . So if a weak property points to a strong property and the strong property is released – the weak property is set to null.
unsafe_retained: Doesn’t get set to nil but set to a dangling location in memory.
While declaring them inline, use double underscore ..
Why is weak needed: To avoid circular references.
Now both have circular references
Installing SAP Trial ( NSP )Posted: February 2, 2014 Filed under: SAP, SAP ABAP Leave a comment
I’ve installed SAP ABAP trial at least a dozen times but keep forgetting some of the points and then end up wasting time trying to set up everything from scratch . I’ll summarize it for future reference as it’s really an easy process.
– Get the NSP trial version from SCN . Google it to get the latest version. Currently, the below URL has the link but who knows what’s the link in future. It should be in “SAP NetWeaver Main Releases’ section.
– Download SAPGUI installer separately. I tried using the one with the main bundle and it doesn’t work . SAP should just take it out to from the main package to remove any confusion.
– Install a JDK ( I installed JDK1.5, update 22 ) – not sure if a JRE will suffice but just to be sure I installed Java SDK SE 1.5 .
– Install MS Loopback adapter.
-Download WINRAR in advance.
-Chrome ( My favourite browser ). I’m simply not used to IE anymore and end up installing Chrome. WIll be helpful to keep it ready.
– Virtualbox – it’s useful to have the OS running as a VM for 2 reasons:
a) It’s easy to take snapshots at stages to revert to a working stage.
b) It’s easy to clone machines. I’ve got 2 clones now – one with a Win 7 VM which can be used to install anything and one with a functional SAP NSP system.
Software Installation Process:
– Have a fresh win7 installation ready – better use a base VM and clone it .
– It’s automatic to share resources between host and client machines on VMs – Copy all the software files to the client machine. Host is the base OS and by client I mean the one running on a VM.
– Install Winrar and unrar the software files.
– Install Java.
-MSLoopback adapter is already installed.
– Start SAP installation . It’s natural for it to log off and do a login again . I
– It will give some warnings about conditions not being met. They can be ignored.
– The installation took around 8 hours with step 16 ( import ABAP taking a lot of time ) . Hence, don’t panic if it stays there for along time.
– Install SAPGUI and add NSP to logon .
– You start the system from SAP MMC.
– I wasn’t able to modify the system params ( icm/host_name_full ) from RZ10 . So I just changed the file at OS level directly and restarted SAP .
– Ensure that the host name ( FQDN ) has a .com ( or dot<something> ) as ABAP checks it while trying to get the host etc and you’ll get a short dump .
– SAP help lists all the services required to be activated .
– If the system is timing out on you ( as it’s not very powerful ) , you can increase the timeout for HTTP service from transaction SMICM :-> Go To Services -> Chose HTTP and change time etc.
This version is definitely better ( and more stable in installation ) compared to the previous ones . It has never failed on me .It has Gateway though I haven’t really done anything with it yet.
Installing license keys and developer key for BCUSER.
– I removed the existing license keys as the system name is SAP-INTERNAL and the access keys for BCUSER seems to take an issue with it.
– Go to SLICENSE, remove the license keys and install the new one ( chose the first NSP from the license key request page ) .
– Once the license is installed, you can then try to create custom objects and enter key for BCUSER.
Troubleshooting adapter module JCo RFC callsPosted: February 2, 2014 Filed under: SAP, SAP ABAP, SAP Java, SAP PI/PO | Tags: ABAP, java, SAP, SAP PI Leave a comment
From my blog on SCN – http://scn.sap.com/community/pi-and-soa-middleware/blog/2013/12/23/troubleshooting-adapter-module-jco-rfc-calls
Many a times we have adapter modules ( AM ) which in turn do a RFC call to ABAP stack of the XI system to retrieve information. This can be handy to make a generic AM that can be plugged in for multiple interfaces.
As an example, if we already have a text file with idoc data in plain text format, the adapter module can be used to convert this data into idoc format. The ABAP stack FM can be created to inquire idoc metadata information in IDX2 and use it to create the idoc structure.
The different steps are as follows:
1.This step shows the data being processed in the module chain. It’s represented in hex format for the message. So, if we have a text file with content “hello” – the message will be “68 65 6c 6c 6f”.
2.The message is entering the module chain. It can be after reading the file for a sender FTP adapter if this is the first module or after another module call e.g. for code page conversion.
3.As part of the adapter module processing, a RFC call is made using Java Connector ( JCo ) with the message and other parameters. These will be adapter module parameters.
4.The returned message is idoc data in hex format of the XML stream.
5.The message is leaving the adapter module.
6.The data is in hex for the idoc. To make it simple, if the idoc data is “<hello>” the message here is “3c 68 65 6c 6c 6f 3e”.
In the above diagram, the module parameters are sent to the RFC function module in text format though the message data will be hex.
With all the above theoretical knowledge, let’s create a simple Java program that can aid in troubleshooting.Pre-requisite Libraries to be added to our project:
1. Google Guava :
Get it from here – http://code.google.com/p/guava-libraries/
2. JCO libs
Get it from service marketplace.
3. Create a jar with the property file: I’ve provided a sample property file. It has the details to make us connect to the host, authenticate
Files to be created:
1. Props.properties : to store connection / authentication details so that it’s easy to change the target instead of hardcoding the values in the program.
2. PropHelper.java : Helper class to read properties file.
3. simulateRFCBean: This is the main class – it’s used for reading the file and making the JCo RFC call.
The steps will be:
1.Check the function module for parameters of type IMPORT (or ask your friendly ABAP colleague about the function module.)
This FM requires two parameters:
SOURCE (the message sent as hexadecimal stream).
SNDPRN (This is a just normal text)
The names won’t have to necessarily match as within the module, we map parameter ‘partner’ to ‘SNDPRN’ for the RFC call.
2.Map the data types to Java using the table mentioned above.
Looking at the function module and the data mapping, we’ll need to
a) Convert the file contents to a hexadecimal string ( byte array in Java )
b) Send the sending system as a string ( String in Java )
3.With the above information, it’s straight forward to create the Java program.
a)Read the JCO properties – PropHelper.java is a helper class to help read these properties instead of hardcoding in the program.
b)Read the file to be checked and convert to byte array.
byte fileData = Files.toByteArray(new File(“C://temp//bad3.txt”));
– Do the necessary JCO Set up, set the parameters to be supplied for the RFC call
and finally, make the call.
Now with the set up done, we’re able to replicate the error scenario.
The issue on the communication channel log indicated.
Using this program, we’re able to replicate the failure.
For debugging on ABAP, an external break-point needs to be set up in the called function module.
Some of the error scenarios we encountered:
- Bad data – new line appearing in the message.
- IDX2 configuration missing for the unique message combination – existing for the basic type and an extension.
However, once we’re able to simulate the failure and debug the issue, finding the resolution is much easier.
Sourcde code link : https://github.com/viksingh/SimulateRFCCalls
Antifragile softwarePosted: February 1, 2014 Filed under: SAP, Software | Tags: ABAP, Nodejs, SAP Leave a comment
From my blog on SCN – http://scn.sap.com/community/abap/blog/2013/12/01/antifragile-software
Before proceeding further, I have a confession to make – it has mostly nothing to do with ABAP development and it even spans other areas of SAP. For simulation of fault tolerance systems, I used non SAP software However, as it concerns software development and in SAP space what better subspace than ABAP to get opinions of developers, I’m putting it in ABAP development. Hopefully it will be of some use.
I recently read “Anti-Fragile” from Nicolas Nassim Taleb and it kept me wrapped till my eyes were hurting. It is a very good read even though I may not agree with all his notions. Taleb coined the term ‘antfragile’ as there was no English word for what he wanted to express, though there’s a mathematical term – long complexity.
Taleb categorizes objects in the following triads:
– Fragile : This is something that doesn’t like volatility. An example will be a package of wine glasses you’re sending to a friend.
– Robust : This is the normal condition of most of the products we expect to work. It will include the wine glasses you’re sending to the friend, our bodies ,computer systems.
– Antifragile: These gain from volatility. It’s performance thrives when confronted with volatility.
Here volatility means an event that induces stress.If fragile loses from volatility and robustness merely tolerates adverse conditions, the object that gains from volatility is antifragile. Our own bodies are healthier over time with non linear exposure to temperature and food. Our immune systems become better when attacked by disease. And as it’s now obvious in Australia, small naturally occurring fires prevent bigger fires. Spider webs are able to resist winds of hurricanes – a single thread breaks allowing the rest of the web to remain unharmed.
Taleb’s book mostly considers the notions of fragility and antifragility in biological, medical, economic, and political systems. He doesn’t talk about how this can apply to software systems but there are some valuable lessons we can draw when it comes to software systems. Failures can result from a variety of causes – mistakes are made and software bugs can be in hibernation for a long time before showing up. As these failures are not predictable, the risk and uncertainty in any system increases with time.In some ways, the problem is similar to a turkey fed by the butcher – for a thousand days, the turkey is fed by the butcher and each day the turkey feels that statistically, the butcher will never hurt him. In fact the confidence is highest just before Thanksgiving.
Traditionally we have been designing software systems trying to make them robust and we expect them to work under all conditions.This is becoming more challenging as software is becoming much more complex and the number of components is increasing. We use technology stacks at higher levels of abstractions. Further, with onset of cloud, there might be parts which are not even in your own direct control. Your office might be safe but what happens if data centers where the data and applications reside get hit by the proverbial truck.
We try to prove the correctness of a system through rigorous analysis using models and lots of testing. However, both are never sufficient and as a result some bugs always show up in production – especially while interacting with other systems.
For designing many systems, we often look at nature – nature is efficient and wouldn’t waste any resources. At the same time, it has anti-fragility built in – when we exercise, we’re temporarily putting stress on body. Consequently, body overshoots in it’s prediction for next stressful condition and we become stronger.If you lift 100 kg, your body prepares itself for lifting 102 kg next time.
We spend a great deal of effort in making a system robust but much in making it antifragile.The rough equivalent of antifragile is resilience in common language – it is an attribute of a system that enables it to deal with failure in a way that doesn’t cause the entire system to fail. There are two ways to increase resilience in systems.
a) Create fault tolerant applications:The following classical best practices aid in this goal.
– Focus is better than features: Keep classes small and focused – they should be created for a specific task and should do it well. If you see new extraneous features being added, it’s better to create separate classes for them.
– Simplicity is better than anything: Keeping the design simple – It may be fun to use dynamic programming using ABAP RTTI / Java Reflection but if it’s not required, don’t do it.
– Keep high cohesion and loose coupling: If the application is tightly coupled, making a change is highly risky.It makes the code harder to understand as it becomes confusing when it’s trying to do two things at the same time ( e.g. try to do data access and execute a business logic at the same time ). Any change to the business logic change will have to rip through data access parts. As an example, whenever the system needs to communicate with an external system ( say you’re sending messages via an ABAP proxy to PI / some external systems ) , keep the sending part as a V2 update. You don’t want to block the main business transaction processing or hang on to locks.If there are issues with the receiving system being slow or non available, it’ll ensure that your main business document processing doesn’t get affected.
And keeping fault tolerance in mind, the following ideas can help.
– While putting any new code in production, make it unpluggable in case things go wrong.
– Create tools to deal with scenarios when things go wrong. Taking the example scenario when we’re not able to send messages as the external system is down / unable to keep up with the throughput, we should have transactions that can resend these messages after identifying them.
Replica Sets and Sharding: As developers we may not have to worry about too much building fault tolerant infrastructure but it’s helpful to know the following concepts.
– Replica Sets: Create a set of replication nodes for redundancy . If the primary node fails the secondary nodes get activated as primary. For instance, in a three node scenario we can have a primary where all the writes happen ( in green ) and the secondaries ( in red )are asynchronously updated. In case the primary fails, one of the secondaries can become the primary. There can be further variations where reads can be delegated to secondaries if freshness of data is not a concern ( e.g. writes to some data set happens very rarely or at times when the likelihood of application requiring data is very small ).
For simulation, I created a replication set and made the primary node fail. This is how things look when things are going on smoothly . dB writes are issued and the callbacks confirm that the write is successful.
Now, I made the primary node fail so that the secondary becomes the primary. We’re issuing inserts but as the secondary takes some time to become primary, the writes are cached in the dB driver before it gets completed and the callbacks confirm of the update.
Sharding: It’s a horizontal partition of data – i.e. divide the data set into multiple servers or shards.
Vertical scaling on contrast aims to add more resources to a single node which is disproportionately more expensive than using smaller systems.
And sharding and replica sets can be combined .
Integration: Here again, some very simple things help a lot.
– Keeping the communication asynchronous – while designing integration always assume that the different parts will go down and identify steps needed to control the impact. It’s similar to the earlier example of primary node failing .
– In queuing scenarios, bad messages to be moved to an error queue. Thankfully this feature has been added in SAP PI with 7.3X .
However, there is a class of errors that we’re still susceptible to – anything which has a single point of failure. And these could be things external to your application – your firewall configuration etc.
Digital circuits achieve fault tolerance with some form of redundancy .An example is triple modular redundancy (TMR).
The majority gate is a simple AND–OR circuit – if the inputs to the majority gate are denoted by x, y and z, then the output of the majority gate is . In essence we have three distinct pipelines and the result is achieved by majority voting.
Application integration with ESB is definitely better than using point to point communications but it’s susceptible to single node failures. May be need a more resilient integration system?
b) Regularly induce failures to reduce uncertainty: Thinking of fault tolerance in design certainly helps but there can always be certain category of problems that come with no warning. Further, the damage is more if a service breaks down once in five years than a service which fails every two weeks. Hence, the assertion is that by making it constantly fail, the impact can be minimized. ‘DR tests’ in enterprises are an effort in that direction. However, what happens if we don’t want the failure to be like a fire drill. And in fact most failures in future are going to be the ones we can’t predict. Companies like netflix are already using this strategy. They have their own Simian Army with different kinds of monkeys – Chaos Monkey shuts down virtual instances in production environment – instanced which are serving live traffic to customers. Chaos Gorilla can bring an entire data center and Chaon Kong will bring down an entire region. Then there is latency monkey – it causes addition of latency and this is a much more difficult problem to deal
Mobile Development and Antifragile
My experience with mobile development is only for the last couple of years but there are some distinct patterns I can see here. The languages, frameworks, technologies etc. are fun than some of the broader points that emerge are:
– Being antifragile is a feature: The expectation of users is to have the application performing even under volatile conditions – bad / low internet connectivity. We went in the application with a lot of features and then cut down to make it more performant – this was the most critical feature.
– Parallels between antifragile and agile development. Agile processes have short iterations, test driven design and rapid prototyping – they all indicate that failure is inherent and the best way to get out of it is to acknowledge and learn from it to make corrections. In some ways, agile is more honest than the traditional methods where we think we can calculate all the future estimates, know all the risks and know what’s going to fail. The emphasis is on failure being a source of strength than something to be hidden assuming it’ll never be discovered.
Cloud and Antifragile
I’ve very limited experience with cloud and none of it is in production- AWS for developer machines , using SAP’s HANA trial for the open sap course and another provider for trying out some other technologies. I can see two big benefits :
– It’s easier to try out new iterations making the software development process more agile.
– If a component fails, it’s easier to replace them.
Thinking of Failure
Moving to the original notion of what’s the most useful – it is the notion of failure . An antifragile way of developing software does require a shift in way of thinking though.Some of the more important ones being :
– Seeing ‘bugs’ differently : Bugs should be seen as how the system functions under certain situation and the emphasis on what we can learn from it.
– Adoption of a ‘blameless’ culture : Follows from the law of unintended consequences. We create incentives for people to come out as perfect who never fail and consequently we annihilate any change, sometimes slowing down to the extent where we can’t even get much needed changes.
These were some of my thoughts. Like any way of thinking, it may not be an elixir but there are valuable lessons in being antifragile.