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can any one explain what is mean by running incremental loading
Running is executing an incremental loading.
QlikView has a script you usually use to load data from external source (like an ETL): you write code in this language to load data from external source (database, files, qvd (qlik propiritary format files, ftp, web)).
Then you run (or execute or reload) this script to load the data in Qlik in memory database.
When you load data from a database table in Qlik you can
- load all data every time the script run (this isn't incremental, is a full load)
or
- load only the changed data from the previous load (this is incremental)
This is a copy from Qlik help
Incremental load is a very common task in relation to data bases. It is defined as loading nothing but new or changed records from the database. All other data should already be available, in one way or another. With QVD Files it is possible to perform incremental load in most cases.
The basic process is described below:
1. Load the new data from Database table (a slow process, but loading a limited number of records).
2. Load the old data from QVD file (loading many records, but a much faster process).
3. Create a new QVD file.
4. Repeat the procedure for every table loaded.
The complexity of the actual solution depends on the nature of the source database, but the following basic cases can be identified:
1) Case 1: Append Only (typically log files
2) Case 2: Insert Only (No Update or Delete)
3) Case 3: Insert and Update (No Delete)
4) Case 4: Insert, Update and Delete
Below you will find outlined solutions for each
how many times we will run for day ?
it depends on your source data and your requirements
If your source data change once at month you don't need to get the source data everyday because the Qlik data and the source (database) data are the same for a month.
If your source data change every day, and you want fresh data in your Qlik database, you need
- a full load every day
- or a full initial load and an incremental (changed data) load every day
Why we need to run?
If you don't run a Qlik reload, your data (in QlikView database) can be older (different) from your source data.
Hi Please check Qlikview help. Clear explanation you can find.
Using QVD Files for Incremental Load
Incremental load is a very common task in relation to data bases. It is defined as loading nothing but new or changed records from the database. All other data should already be available, in one way or another. With QVD Files it is possible to perform incremental load in most cases.
The basic process is described below:
1. Load the new data from Database table (a slow process, but loading a limited number of records).
2. Load the old data from QVD file (loading many records, but a much faster process).
3. Create a new QVD file.
4. Repeat the procedure for every table loaded.
The complexity of the actual solution depends on the nature of the source database, but the following basic cases can be identified:
1) Case 1: Append Only (typically log files
2) Case 2: Insert Only (No Update or Delete)
3) Case 3: Insert and Update (No Delete)
4) Case 4: Insert, Update and Delete
Below you will find outlined solutions for each of these cases. The reading of QVD files can be done in either optimized mode or standard mode. (The method employed is automatically selected by the QlikView script engine depending on the complexity of the operation.) Optimized mode is (very approximately) about 10x faster than standard mode or about 100x faster than loading the database in the ordinary fashion.
Case 1: Append Only
The simplest case is the one of log files; files in which records are only appended and never deleted. The following conditions apply:
- The database must be a log file (or some other file in which records are appended and not inserted or deleted) which is contained in a text file (no ODBC/OLE DB).
- QlikView keeps track of the number of records that have been previously read and loads only records added at the end of the file.
Script Example:
Buffer (Incremental) Load * From LogFile.txt (ansi, txt, delimiter is '\t', embedded labels);
Case 2: Insert Only (No Update or Delete)
If the data resides in a database other than a simple log file the case 1 approach will not work. However, the problem can still be solved with minimum amount of extra work. The following conditions apply:
- The data source can be any database.
- QlikView loads records inserted in the database after the last script execution.
- A field ModificationDate (or similar) is required for QlikView to recognize which records are new.
Script Example:
QV_Table:
SQL SELECT PrimaryKey, X, Y FROM DB_TABLE
WHERE ModificationTime >= #$(LastExecTime)#
AND ModificationTime < #$(BeginningThisExecTime)#;
Concatenate LOAD PrimaryKey, X, Y FROM File.QVD;
STORE QV_Table INTO File.QVD;
(The hash signs in the SQL WHERE clause define the beginning and end of a date. Check your database manual for the correct date syntax for your database.)
Case 3: Insert and Update (No Delete)
The next case is applicable when data in previously loaded records may have changed between script executions. The following conditions apply:
- The data source can be any database.
- QlikView loads records inserted into the database or updated in the database after the last script execution
- A field ModificationDate (or similar) is required for QlikView to recognize which records are new.
- A primary key field is required for QlikView to sort out updated records from the QVD file.
- This solution will force the reading of the QVD file to standard mode (rather than optimized), which is still considerably faster than loading the entire database.
Script Example:
QV_Table:
SQL SELECT PrimaryKey, X, Y FROM DB_TABLE
WHERE ModificationTime >= #$(LastExecTime)#;
Concatenate LOAD PrimaryKey, X, Y FROM File.QVD
WHERE NOT Exists(PrimaryKey);
STORE QV_Table INTO File.QVD;
Case 4: Insert, Update and Delete
The most difficult case to handle is when records are actually deleted from the source database between script executions. The following conditions apply:
- The data source can be any database.
- QlikView loads records inserted into the database or updated in the database after the last script execution.
- QlikView removes records deleted from the database after the last script execution.
- A field ModificationDate (or similar) is required for QlikView to recognize which records are new.
- A primary key field is required for QlikView to sort out updated records from the QVD file.
- This solution will force the reading of the QVD file to standard mode (rather than optimized), which is still considerably faster than loading the entire database.
Script Example:
Let ThisExecTime = Now( );
QV_Table:
SQL SELECT PrimaryKey, X, Y FROM DB_TABLE
WHERE ModificationTime >= #$(LastExecTime)#
AND ModificationTime < #$(ThisExecTime)#;
Concatenate LOAD PrimaryKey, X, Y FROM File.QVD
WHERE NOT EXISTS(PrimaryKey);
Inner Join SQL SELECT PrimaryKey FROM DB_TABLE;
If ScriptErrorCount = 0 then
STORE QV_Table INTO File.QVD;
Let LastExecTime = ThisExecTime;
End If