Java regex Matcher’s first group is the whole pattern

I didn’t realize that Java’s regex class, Matcher, uses to denote the entire pattern. I spent some time debugging it. Hence this note.

As is stated in the documentation, “Capturing groups are indexed from left to right, starting at one. Group zero denotes the entire pattern, so the expression is equivalent to”

Here is a sample code to pick out twitter user names out of a string using Java. A set is returned, therefore if a user name is mentioned more than once, it’ll only be stored once in the set. All user names are returned back in lowercase. This function has gone through pretty through testing and works pretty well.

In addition, this is also a pretty good sample of negative lookbehind regex usage: we are not looking for pattern where @ is proceeded by any valid Twitter user name character.

Update: Angle brackets in Java code caused my code formatter to add some junk inside the code. Be aware! I need to look for a good code formatter for WordPress…


import java.util.HashSet;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Tweet {

     * Get usernames mentioned in a string.
     * @param s
     *          string, a tweet
     * @return the set of usernames mentioned in the text of the tweet.
     *         A username-mention is "@" followed by a Twitter username
     *         A Twitter username is composed of:
     *          English letters, digits, dash, and underscore
     *         The username-mention cannot be immediately preceded or followed
     *         by any character valid in a Twitter username. Therefore:
     * does NOT contain a mention of the username example.
     *         Twitter usernames are case-insensitive
    public static Set<string> getMentionedUsersFromString(String s) {
        Set</string><string> set = new HashSet</string><string>();
         String pattern = "(?< ![a-zA-Z0-9_-])@([a-zA-Z0-9_-]+)";    // see spec above 
        Matcher m = Pattern.compile(pattern).matcher(s);
        while (m.find()) {
        return set;

No 32-bit for SQL Server 2016 Express

I’ve learned that SQL Server 2016 Standard and Enterprise Editions no longer provide 32-bit. But I do wonder about SQL Server 2016 Express Edition. It’s different in that it’s free, and mostly geared toward lightweight usage, people who are learning, etc. So perhaps it still offers 32-bit?

After some upgrade work to one SQL Server 2008 R2 Express 32-bit, I can tell you with real experience that SQL Server 2016 Express does NOT have 64-bit either.

So the latest Express edition that has 32-bit is SQL Server 2014. Like Allan Hirt, I also say good riddance. It’s time to move on.

Adding attachment to Outlook 2016 email

A couple of months ago Outlook 2016 on my old PC (Windows 10) started misbehaving:

  • Clicking “Attach File” to add an attachment from my PC to an email message;
  • A window would show up. When it worked, I would be able to move the mouse down and click “Browse This PC…”. However, nowadays this window disappears so quickly that it doesn’t give me enough time to click that “Browse This PC…” item!
  • Web search ensued. Some suggested repairing the mailbox, which I’ve done but to no avail;
  • To get around this, open a windows Explorer window and navigate to the location where the attachment is located, drag it to the email window and release it. Viola, attachment added and you’re done!

Hope this helps!

SQL Server best practice: grant permissions to per-service SID

Since Windows Server 2008/Windows Vista, from SQL Server 2008 onward, SQL Server installation process automatically generates per-service security identifier (SID). Whenever possible, it is recommended to grant rights to this service SID for security reasons, instead of your SQL Server’s startup account, which typically is domain user account.

For example, for performance reasons, I always want to SQL Server to have the following rights: Instant File Initialization and Lock Pages in Memory. The former enables instantaneous data (not log) file growth; whereas the later prevents Windows system from paging SQL Server data to virtual memory on disk.

Those rights can be granted via the Local Security Policy application, secpol.msc. Navigate to Security Settings -> Local Policies -> User Rights Assignment, you’ll find them there. Please note that Instant File Initialization is actually called “Perform volume maintenance tasks”.

Before service SID was introduced, I always granted those rights to SQL Server’s startup account. In my case it was typically a domain\user account. With the introduction of service SID, SQL Server’s resource access rights is the sum of both its startup account and service SID. Therefore it is recommended to grant rights to service SID, for obvious security reasons.

To prove that’s the case, let’s conduct the following experiment. For default instance of SQL Server, its service SID is NT Service\MSSQLSERVER. For named instance, its service SID is NT Service\MSSQL$InstanceName. Please note instant file initialization, once enabled, only works for SQL Server data files, not logs.

1. Assume your SQL Server instance is running under a domain\user account without “Perform volume maintenance tasks”;
2. Run the following code:

dbcc traceon(3004,3605,-1)
create database TestDb
exec sp_readerrorlog
drop database TestDb
dbcc traceoff(3004,3605,-1)

Pay attention to the output of “exec sp_readerrorlog”. You should see something similar to this:

2016-05-19 23:39:35.830 spid51 Zeroing C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\TestDb.mdf from page 0 to 1024 (0x0 to 0x800000)
2016-05-19 23:39:35.890 spid51 Zeroing completed on C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\TestDb.mdf (elapsed = 66 ms)

3. Now using secpol.msc, grant your service SID, in my case, NT Service\MSSQLSERVER, the right of “Perform volume maintenance tasks”;
4. Restart SQL Server instance;
5. Repeat step 2, you shouldn’t see entry similar to the one listed above in the error log, indicating that SQL Server has the combined rights of its startup account and its service SID.

By the way, this also applies to data and log folder permissions. Only grant data and log folder permissions to service SID, not its startup account. I have automated that process here.

Happy learning!