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Storage engine differences in Software Access barcode pdf417 in Software Storage engine differences




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Storage engine differences using barcode implementation for software control to generate, create pdf417 2d barcode image in software applications. Intelligent Mail We will not Software PDF 417 go into much detail here about the differences between the MyISAM and the InnoDB storage engines offered by MySQL. However, regarding indexes there are some important differences to know between MySQL"s two most important storage engines. They influence some decisions you will have to make.

. 2 . MyISAM In the figu re below you can see a simplified schema of how indexes work with the MyISAM storage engine. Their most important property can be summed up as "all indexes are created equal". This means that there is no technical difference between the primary and secondary keys.

. MyISAM Inde PDF417 for None xing Schematics Index 1 (Primary Key) isbn 2-345-6 7-234-5 8-456-7 ...

ordered by ISBN column (2) (1) (3) ...

number of row in the data area Row pointers from each index"s entries point to the actual data record. The more indexes are defined, the more expensive INSERT, UPDATE and DELETE become, because in addition t o the actual data table, all the inde need to xes be amended with the new entries and their row pointers. rowpointer.

Index 2 (ID X_TITLE) title Concurrency...

Effective Java Moby Dick ...

ordered by title column (3) (2) (1) ...

number of row in the data area rowpointer isbn 7-234-5 2-345-6 8-456-7 ...

. BOOKS (Data pdf417 for None Table) title Moby Dick Effective Java Concurrency...

...

author Melville Bloch Goetz ...

Random order (order of insertion). Index 3 (ID X_AUTHOR) author Bloch Goetz Melville ...

ordered by author column (2) (3) (1) ...

number of row in the data area rowpointer Finding an author through IDX_AUTHOR is quick, because it is sorted by the person"s name. The book details are then found with a second step, following the row pointer to the correct data record..

The diagram PDF417 for None shows a single (theoretical) data table called books. It has three columns named isbn, title, and author. This is a very simple schema, but it is sufficient for explanation purposes.

The exact definition can be found in the Adding indexes to tables recipe in this chapter. For now, it is not important. MyISAM tables store information in the order it is inserted.

In the example, there are three records representing a single book each. The ISBN number is declared as the primary key for this table. As you can see, the records are not ordered in the table itself the ISBN numbers are out of what would be their lexical order.

Let"s assume they have been inserted by someone in this order.. Indexing No w, have a look at the first index the PRIMARY KEY. The index is sorted by the isbn column. Associated with each index entry is a row pointer that leads to the actual data record in the books table.

When looking up a specific ISBN number in the primary key index, the database server follows the row pointer to retrieve the remaining data fields. The same holds true for the other two indexes IDX_TITLE and IDX_AUTHOR, which are sorted by the respective fields and also contain a row pointer each. Looking up a book"s details by any one of the three possible search criteria is a two-part operation: first, find the index record, and then follow the row pointer to get the rest of the data.

With this technique you can insert data very quickly because the actual data records are simply appended to the table. Only the relatively small index records need to be kept in order, meaning much less data has to be shuffled around on the disk. There are drawbacks to this approach as well.

Even in cases where you only ever want to look up data by a single search column, there will be two accesses to the storage subsystem one for the index, another for the data..
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