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What is the best practice to manage time intervals in Oracle? For example: I have a room that will be rented between 8:15 till 9:00. So I have at least 2 fields: dt_start and dt_end, I suppose. I can not permit to enter a rent between 8:45 till 9:20. So how would be the best table structure for that? Thanks
There is no clear consensus on the best way to implement this. The answer certainly depends a great deal on your exact situation. The options are:
Table with unique constraint on ROOM_ID and a block of time. This is only realistic if the application allocates a reasonably small amount of time using reasonably large blocks. For example, if a room can only be allocated for at most a week, 5 minutes at a time. But if reservations are to the second, and can span over a year, this would require 31 million rows for one reservation.
Trigger. Avoid this solution if possible. The chance of implementing this logic in a trigger that is both consistent and concurrent is very low.
Materialized view. This is my preferred approach. For example, see my answer here.
Enforced by the application. This only works if the application can serialize access and if no ad hoc SQL is allowed.
Commercial Tool. For example, RuleGen.
BEFORE INSERT TRIGGER is the best way to accomplish your need.
In trigger, figure out that the new time is not conflicting the current time of your particular room, and if so you can Rais Error, otherwise let the update happen.
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Currently, in our project, we are using Informatica for Data loading.
We have a requirement to load 100 tables (in future it will increase) and each has 100 Million records, and we need to perform delta operation on that. What might be the best way to perform this operation in an efficient way?
If it's possible, try truncate and load. This way after each run you will have a full, fresh dump.
If you can't truncate the targets and need the delta, get some timestamp or counter that will allow to read modified rows only - like new and updated. Some "upddated date". This way you will limit the number of data being read. This will not let you do the deletes, though. So...
Create a separate flow for seeking deleted rows, that will not read the full row, but IDs only. This will still need to check all rows, but limited to just one column, so as a result it should be quite efficient. Use it to delete rows in target - or just to mark them as deleted.
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Collecting Stats in oracle- How Performance gets improved?
When doing collect stats on fields/indexes , system collects the information like: total row counts of the table, how many distinct values are there in the column, how many rows per value, is the column indexed, if so unique or non unique etc
The above information are known as statistics.
1.How Performance gets improved?
2.How does the Parsing Engine/Cost Based Optimizer(CBO) use the statistics for the better performance of a query?
3.Why do i need to collect stats on the indexed columns , despite the fact
using indexed columns in where clause/joins itself will give better performance?
The above information are known as statistics. so How Performance gets improved?
Because the more and accurate information will let the optimizer decide for a better execution plan.
For example,
When you try to reach your destination for the first time, you gather information about the routes, directions, landmark etc. Once you reach your destination, you have all the information gathered, and the next time you would reach your destination using the shortest path or the best way to reach in least time.
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We have standard issue tracking system (home grown for internal use only) and plan to add planing capabilities as all task have all necessary data to make estimation.
So each task have:
more or less accurate estimated time
accurate spent time
more or less accurate percentage completeness
accurate beginning/schedule date
task owner
Also we have scheduled version which is a group of tasks.
We don't know how to ask to question:
how many hours we must spend to release end
according to tasks time data and version schedule date?
or:
do we finish version to specified schedule?
PS Seems that percentage completeness is less accurate and we decide to drop it...
Estimation is trickier than it looks. For example, when people are asked to give time estimates, they generally systematically underestimate (it's called "optimism bias").
My best suggestion is that you should get a book on the topic and read it. McConnell's Software Estimation: Demystifying the Black Art is a good place to start.
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4 years ago, I've built a webapp which is still used by some friends. the problem with that app, is that now it has a huge database, and it loads very slow. I know that is just my fault, mysql queries are mixted all over the places(even in the layout generation time).
ATM I know some about OO. I'll like to use this knowledge in my old app, but I don't know how to do it without rewriting all the from the beginning. Using MVC for my app, is very difficult at this moment.
If you were in my place, or if you will had the task to improve the speed of my old app, how you will do it? Do you have any tips for me? Any working scenarios?
It all depends on context. The best would be to change the entire application, introducing best practices and standards at once. But perhaps would be better to adopt an evolutionary approach:
1- Identify the major bottlenecks in the application using a profiling tool or load test.
2 - Estimate the effort required to refactoring each item.
3 - Identify the pages for which performance is more sensitive to the end user.
4 - Based on the information identified create a task list and set the priority of each item.
Attack one prolem at a time, making small increments. Always trying to spend 80% of your time solving the 20% more critical problems.
Hard to give specific advice without a specific question, but here are some general optimization/organization techniques:
Profile to find hot spots in your code
you mention mysql queries being slow to load, try to optimize them
possibly move data base access to stored procedures to help modularize your code
look for repeated code and try to move it to objects one piece at a time
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In our projects we are often asked to give ball park estimates for activities. My question does it really help in taking decisions based on the estimate.
Yes as pointed out above.
No if the client later says "Oh, but that's much more than the X days you initially estimated"
You need to be careful in explaining and agreeing on what "ballpark" really means
Yes .. it can help to give rough estimates to the client but later on these estimates can show upto +/- 50% variation.
But it can help to gauge the size of the project and roughly manday efforts
Something to add to the existing responses.
Pros:
Helpful for a teamleader to assess
the number of resources needed for a
set of activities.
Useful to assess
whether a task would fit in a pre
defined timeline
Cons:
Very rough estimate
Need to be very careful while sharing with the customer.
I often use these ballpark estimates to give a quick price quote to a client, when based on models such as WMFP or COCOMO-II they can also help me make an unbiased assessment.