Coding Cheatsheets

Coding and problem-solving skills are essential for delivering high-quality software applications. Some good practices:

1. Modular and Efficient Code — Reuse code by writing common functions. Helps with code optimization.
2. Null checks — Guard clause for validation: check null and return. Proper variable names, null & length checks, set default values wherever possible.
3. Memory handling — Needs to be done in C programming code.
4. Initialize/Reset variables — Especially in nested while loops.
5. Write Code Comments — Makes it easy to read and understand logic. Helps maintain defect-free code.
6. Make code configurable — For attributes whose values might change.
7. Refer cache — In order to reduce database calls for better performance.
8. Code reviews by peers — Helps us learn from each other and improve skills.
9. Analyse log files — To troubleshoot issues.
10. Happy Coding — Write great code and use great languages.

Other tips:

• Embrace simplicity and avoid unnecessary complexity
• Use built-in features and libraries
• Be mindful of performance
• Prioritize human readability; write comments for understanding
• Use meaningful variable names
• VSCode is an excellent code editor. GitHub Copilot can be enabled for AI-assisted coding.

Code snippets for strcmp(), sprintf():

if(str1 && str2 && strcmp(str1, str2) == 0)
{
    sprintf(printbuff, "str1 and str2 are same: %s and %s\n", str1, str2);
}

strstr() & sscanf():

if(str1 && str2 && strstr(str1, str2) != NULL) {
    sprintf(printfbuff, "str2 is present in str1\n");
    sscanf(str1, "%2d", strmmdd); //read first 2 chars from str1 into integer strmmdd
}

The struct tm represents date and time information — used for manipulating and formatting time-related data:

time_t epoch_time = <time-unixtimestamp>
struct tm new_tm = localtime(&epoch_time); //store unix timestamp into struct tm

//Adjust new_tm
new_tm->tm_mon  = <month>;
new_tm->tm_year = <year>;
new_tm->tm_mday = <dayofmonth>;
new_tm->tm_hour = 0;
new_tm->tm_min  = 0;
new_tm->tm_sec  = 0;
new_tm->tm_isdst = -1;

time_t new_unixtime = mktime(&new_tm); //convert struct tm back to epoch

Annotations help avoid writing boilerplate code and improve coding efficiency. Common Java Annotations:

Note: Lombok is a Java library that generates known patterns of code, allowing us to reduce boilerplate.

Search string/pattern using grep commands:

Other important Unix commands:

Git is widely used as a version control system. Below commands help in managing files in Git:

Key points to consider for Oracle SQL tuning:

1. SELECT query tuning — Validate using "Explain Plan" in SQL Developer.
   • Parallel hint (/*+ parallel(8) */) with increased thread count for faster processing.
   • Use columns with index in WHERE clause.
   • Use DB partitions to query data.
   • Use WITH clause for queries to make future changes easier.
   • Use EXISTS instead of COUNT.
   • Leverage Oracle JSON functions (JSON_ARRAYAGG, JSON_VALUE) for multiple column selection.
2. PL/SQL Performance — Use BULK COLLECT and FORALL for bulk DML updates to reduce context switching.
3. Oracle SQL Developer shortcuts:
   • Ctrl+F7: Format SQL query
   • Shift+F4: Opens describe window for current object/table at cursor
   • F10: SQL cost estimate (Explain Plan)
   • Export data to XLS or clipboard
   • Import data using sqlldr utility from Unix (faster than insert queries)

If any Oracle Database transaction is taking longer than expected, the DB query processing is likely stuck or waiting for another session to complete.

• Fetch blocking sessions due to table lock:

  select (select username from v$session where sid=a.sid) blocker, a.sid,
         ' is blocking ',
         (select username from v$session where sid=b.sid) blockee, b.sid
  from v$lock a, v$lock b
  where a.block = 1 and b.request > 0 and a.id1 = b.id1 and a.id2 = b.id2;

• Percentage completion of long-running sessions:

  select sid, to_char(start_time,'hh24:mi:ss') stime, message,
         (sofar/totalwork) * 100 percent
  from v$session_longops where sofar/totalwork < 1;

• Fetch active DB sessions:

  select S.USERNAME, s.sid, s.osuser, t.sql_id, sql_text
  from v$sqltext_with_newlines t, V$SESSION s
  where t.address = s.sql_address and t.hash_value = s.sql_hash_value
    and s.status = 'ACTIVE' and s.username <> 'SYSTEM'
  order by s.sid, t.piece;

• Kill DB session (if needed):

  select username, sid, serial# from v$session where sid=xxxx;
  alter system kill session 'sid#,serial#';