Lightning Experience is a modern CRM user interface optimized for speed. A component-based framework that allow you to build reusable components to customize the Lightning Experience. Drag-and-drop technologies for fast and easy app building & customization. You can create a custom Lightning tab that points to your component and include that tab in your Salesforce1 Mobile navigation. We already have Visualforce components, they are page-centric and most of the work is done on the server. Lightning is designed from the component up, rather than having the concept of a page as its fundamental unit. Lightning Components are client-side centric, which makes them more dynamic and mobile-friendly. You can also use Lightening Components in Visualforce Pages, see this.
From Setup in Salesforce Classic, click Lightning Experience. On the Lightning Experience Migration Assistant page, click the Lightning Experience button to set it to Enable.

The Concurrent Apex Limit exceeded issue is big issue in large data Orgs or implementations without following best practices. Exception generally received by end user or Admin:

"Unable to Process Request. Concurrent requests limit exceeded.
To protect all customers from excessive usage and Denial of Service attacks, we limit the number of long-running requests that are processed at the same time by an organization. Your request has been denied because this limit has been exceeded by your organization. Please try your request again later."

Salesforce Developer Blog Says:

The multitenant Force.com platform uses governor limits to ensure that system resources are available to all customers and to prevent any one customer from monopolizing them. If a governor limit is exceeded, the associated execution governor limit issues a runtime exception that cannot be handled. When you design your applications, you can help plan for their growth by keeping these limits in mind.

One of the limits customers frequently reach is the concurrent request limit. Once a synchronous Apex request runs longer than 5 seconds, it begins counting against this limit. Each organization is allowed 10 concurrent long-running requests. If the limit is reached, any new synchronous Apex request results in a runtime exception. This behavior occurs until the organization’s requests are below the limit.

Ultimately, this limit is in place to protect the user experience. Would you want your users waiting 5 seconds or more for a page to load?

So how would you know which operation is taking time? Even you can track it through Debug logs using many filter Extensions like 'Salesforce Debug Logs Analyzer'. One more level is Salesforce Event Log, obviously you should have access of it.

Go to https://salesforce-elf.herokuapp.com/

Login with your Salesforce Sandbox or Production login. Select dates range and apply, now you can download Salesforce Event Log File by Event Type.

Open in excel and Sort by Execution Time and see where its taking time, optimize that using best practice or adjusting business rules.

If the cause was a high callout time, you can filter your ApexExecution file based on QUIDDITY (E, H, M, R, V, W, X, L, K, or I) and CALLOUT_TIME (>5000), both of which were added in the Spring '16 release.

The values for quiddity in the logs include:

A - Legacy Batch Apex
C - Schedule Apex
E - Inbound Email Service
F - Future
H - Apex REST
I - Invocable Action
K - Quick Action
L - Aura
M - Remote Action
Q - Queuable
R - Synchronous
S - Serial Batch Apex
T - Apex Tests
TS - Synchronous Apex Tests
TA - Asynchronous Apex Tests
V - Visualforce
W - SOAP Webservices
X - Execute Anonymous

Guest site user debug is not showing in debug log, it is related to Winter 17 change. Now need to set a special cookie from their side so that Salesforce will generate logs only when that user accesses the site.

Public users generate a large volume of events, which can quickly fill up your debug logs. For this reason, logs are collected for site visitors who are using your Guest User license only when a public user’s browser has a special cookie. This feature is available in both Lightning Experience and Salesforce Classic.

The debug logs are collected for site visitors who are using the Guest User license only when a public user’s browser has a special cookie.

The value of the cookie should be
Name : debug_logs
Value: debug_logs
domain: .force.com

To set this cookie via Chrome, Navigate to the Site URL,
Go to Developer tools and then to Console tab, Execute the below java-script
document.cookie ="debug_logs=debug_logs;domain=.force.com";

Also if you access the site using API, you can set the cookie in the same format. For example, when connecting to the site using JAVA, you can
use URLConnection class and set the cookie value as below

URL url = new URL("http://*********-developer-edition.gus.force.com/");
URLConnection con = url.openConnection();
con.setDoOutput(true);
con.setRequestProperty("Cookie", "debug_logs=debug_logs,domain=.force.com");
con.setRequestProperty("Content-Type", "text/plain; charset=utf-8");
con.connect();

Changes that improve your experience with Communities.

General Enhancements

The DISTANCE function is now supported with location-based queries. You can calculate the distance between two location values, such as between a warehouse and a store.

DISTANCE() now works with location and address fields. You can retrieve a specific distance (say, of a store from a contact’s location) and display it to the user.

For example: With custom development, geocodes can unlock a whole new way to understand your customers and run your business. Here are some cool use cases that could be solved using geocodes: 

Now you can edit your existing chatter posts containing files or links. Before Summer 16 you have to comment if you missed mentions in posts.

Follow steps below to enable this feature:

• Setup | 
• Build | 
• Customize | 
• Chatter | 
• Chatter Settings |
• Select Allow users to edit posts and comments check-box.

In Summer 16, now you can see record details on hover in List view.

To enable Responsive List Hovers, follow below steps:

• In Setup, select Create | Apps, and find the name of the console you want to modify.
• Click Edit.
• Select Enable Responsive Lists.
• Click Save.

See preview without opening record!

In Summer 16 Global Picklist and Strictly enforce picklist values functionality is added!

Global Picklist can added by following steps:

• From Setup, enter Picklists in the Quick Find box, then select Picklists.
• Next to Global Picklists, click New.
• Enter a label for the global picklist. This name appears in Setup, and when users create a picklist based on this global picklist.
• To tell admins what this set of values is for, enter a specific description of the global picklist. This text appears on the Picklists list page in Setup.
• Click Save.
• In the Picklist Value Set section, click New.
• Add picklist values by clicking New, then entering the values one per line.
• Click Save.
• To reorder the values, click Reorder. Optionally, choose to sort values alphabetically or to use the first value as the default value.

Use to comparing the field on related object.

Syntax:
VLOOKUP(field_to_return, field_on_lookup_object, lookup_value)

Create a validation rule and pass parameters, field_to_return, field_on_lookup_object & lookup_value.

Field_to_return : The field that contains the value you want returned
Field_on_lookup_object : The field on the related object that contains the value want to match
Lookup_value : The value want to match.

For example:

Country(1st object):

Fields:

Name(Text)
Capital(Text)

Customer(2nd object):

Fields:

Queueable Apex is essentially a superset of future methods with some extra features, released in Winter 15. We can say its a mixer of future methods and the power of Batch Apex! It is called by a simpleSystem.enqueueJob() method, which returns a job ID like Apex batch that you can monitor.
Queueable Apex allows following additional benefits:

TEMPLATE NOT FOUND issue due to non access of field in email Templates. Salesforce is saying that Email Template is using standard controller even for Visualforce templates using without sharing classes. So you can't send email through template if user don't have access of fields used in template!

Send email from Apex is counting against limit of email send so its necessary to send email through email template by workflow. We tried a work around and its working fine. Follow following steps:

1. Make a field on object from where email need to send.
2. Make a workflow that send email on change of above field you made.
3. Use email template that contains above made field in template.
4. Populate field when condition matched or need to send email.

As we know Continuation is used for asynchronous callouts to make long-running requests from a Visualforce page to an external Web service and process responses in callback methods. Asynchronous callouts that are made from a Visualforce page don’t count toward the Apex limit of 10 synchronous requests that last longer than five seconds.

An asynchronous callout should made from a Visualforce page and the response is returned through a callback method. So you cannot use a method that is not called from Visualforce page, but we can use action method to call Continuation callout.

When repeating action need to perform then action function is only way for asynchronous callout of Continuation.

Salesforce URL shortcuts for tabs!

You can use the System.schedule method, which takes a cron string to represent the repeating time.

Execute below code to run batch on every 15th minutes of hours.

String CRON_EXP = '0 15 * * * ?';
testSchedule sch = new testSchedule();
system.schedule('Test Schedule', CRON_EXP, sch);

Changes 15 to schedule as your requirement!

For Hourly on 0 minute use below code:

String CRON_EXP = '0 0 * * * ?';
testSchedule sch = new testSchedule();
system.schedule('Test Schedule', CRON_EXP, sch);

In default community pages left side bar showing Search box and Recent Items are sometimes giving access to some unwanted records. Here is a work around to hide then.

Make a HTML file and following JQuery to hide left panel.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript">

System mode -

• Its running apex code by ignoring user's permissions. So if logged in user does not have create permission but they will able to create a record.
• Apex code has access to all objects and fields, sharing rules aren't applied for the current user. 
• All apex code run in system mode. It ignores user's permissions. Only exception is anonymous blocks like developer console and standard controllers.

The most confusing and always been part of discussion where the answer is not satisfactory!

With sharing & Without sharing in Apex.

Remember theses points:

• If nothing mentioned in class then default is "Without sharing".
• If nothing defined in class and called within other class then it will execute with calling class's sharing setting accordingly.
• The sharing setting applies to all code contained with in the class, including initialization code, constructors, and methods.
• Inner classes do not inherit the sharing setting from their container class.
• If a with sharing class calls a without sharing class, then the called method(s) will be executed in the mode of the class in which they were defined, in this case, the called method(s) will execute in without sharing mode.
• The 'without sharing' keyword is to ensure that the sharing rules (not permissions) for the current user are not enforced.
• The with sharing keyword allows you to specify that the sharing rules (and not permissions) for the current user be taken into account for a class. You have to explicitly set this keyword for the class because Apex code runs in system mode.

Campaign History Tracking Idea is still waiting to implementation. You can vote here for this: https://success.salesforce.com/ideaView?id=08730000000BqXRAA0

It can be achived using custom fields and either a Workflow, Process Builder or Apex Trigger, but by without code you could use Chatter Feed Tracking instead!

Go to Customize > Chatter > Feed tracking and enable Campaign fields to track.

Now you can see field changes history in Chatter Feed.

You can use the System.schedule method, which takes a cron string to represent the repeating time.

Key is to create string expression that will result in firing every two hours:
Something like:

0 0 1,3,5,7,9,13,15,17,19,21,23 * * ?

• Pictorial representation of internet is Cloud.
• Cloud Computing is nothing but internet computing.
• With this approach everything can be done in internet, no need of any minimum hardware requirements and no need to install any software in local system.
• Cloud Computing is an approach to provide the following services:-
• SAAS (Software As A Service)
• PAAS (Platform As A Service)
• IAAS (Infrastructure As A Service)

Tab is a user interface component to user creates to display custom object data.

There are three type of tabs.

• Custom Tabs
• Visual force Tabs
• Web Tabs