What Is Static And Dynamic Hashing?

The word, 'static' means that something stays still, so by this definition static hashing is the method by which items that are stored in a table, or directory, are fixed. Once these primary pages are full, an overflow bucket is necessary in order to store any additional records, but this must hash to the original bucket (the place where the original records are kept). This can be achieved by using a link to the overflow page, or by using a linked list of the overflow pages.

In the search, the first item that has been saved is the key item and becomes the function value. This is stored as a table code for function calculation. When searching for items, if the key codes are the same then a successful search can be made, either in the original pages or in the overflow buckets. The original bucket is searched initially for a record, and then the overflow buckets are searched; if there are many keys that hash to the same bucket, finding what you require will take longer because many pages will be accessed before you find your record.

This time consuming search method has been solved by using dynamic hashing. Dynamic hashing means that the directory will become bigger in conjunction with the number of collisions, so that new records can be accommodated. This also means that long overflow page chains can be avoided. Linear hashing and extendible hashing are two examples of dynamic hashing techniques.

Hashing is a method of storing records in an organized manner such that each record is hashed with the help of a hash function which gives the location at which the record should be stored.  Eg: We have 5 records : 15,23,36,71,99  suppose we have a hash function nMOD10  record 1 will be  stored at 15MOD10 i.e 5th location and so on....now if we had one more record 25 it would again be stored at location 5 which causes collision.We can use open chaining,and many other methods to solve this problem.

Its a long topic