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Does null take space in MySQL?
While a NULL itself does not require any storage space, NDB reserves 4 bytes per row if the table definition contains any columns allowing NULL , up to 32 NULL columns. (If an NDB Cluster table is defined with more than 32 NULL columns up to 64 NULL columns, then 8 bytes per row are reserved.)
How do I reclaim space in InnoDB?
You can run ALTER TABLE with ENGINE=INNODB which will re-create the table and reclaim the space.
Will truncate free the space?
When a table is truncated, it is dropped and re-created in a new . ibd file, and the freed space is returned to the operating system. Truncating tables that are stored in the system tablespace (tables created when innodb_file_per_table=OFF ) or in a general tablespace leaves blocks of unused space in the tablespace.
Does truncate free up space?
Truncating a table does not give any free space back to the disk – you need to run a SHRINKDATABASE operation for the allocated space to be successfully de-allocated and returned to the disk. Also, as others have mentioned, maybe the table was not taking up much space in the first place.
Does Null value occupy space?
If the field is variable width the NULL value takes up no space. In addition to the space required to store a null value there is also an overhead for having a nullable column. For each row one bit is used per nullable column to mark whether the value for that column is null or not.
How to reclaim disk space in MySQL database?
This might re-pack the rows, fitting more rows into each page if you’ve changed values to NULL. It would be more effective to DELETE rows you don’t need, and then OPTIMIZE TABLE. This will eliminate whole pages, instead of leaving them fragmented.
How much free disk space does MySQL have?
EDIT 1 : I deleted 90% of rows from table then I ran OPTIMIZE TABLE table_name but it has reduced only 4GB of disk space and it is not reclaiming the free disk space. EDIT 2 I even deleted my database and created new DB and table but MySql server still showing 80GB disk space.
How can I save space in MySQL database?
The answer is complex. You can save space by using NULL instead of real values. InnoDB uses only 1 bit per column per row to indicate that the value is NULL (see my old answer to https://stackoverflow.com/a/230923/20860) for details.
How big should MySQL key _ block _ size be?
This can do marvels on the size of your table especially if there is a lot of text and if you use smaller KEY_BLOCK_SIZE such as 8K or even 4K (the default is 16K). You can also check out how much space you can gain from multiple benchmarks regarding this issue on other blogs but MySQL documentation advertises 25% to 50% (it was almost 90% for me).