Physical Characteristics of MEMORY Tables-opracowanie

Physical Characteristics of MEMORY Tables
The MEMORY storage engine associates each table with one disk file, which stores the table definition
(not the data). The file name begins with the table name and has an extension of .frm.
MEMORY tables have the following characteristics:
• Space for MEMORY tables is allocated in small blocks. Tables use 100% dynamic hashing for inserts.
No overflow area or extra key space is needed. No extra space is needed for free lists. Deleted rows
are put in a linked list and are reused when you insert new data into the table. MEMORY tables also
have none of the problems commonly associated with deletes plus inserts in hashed tables.
• MEMORY tables use a fixed-length row-storage format. Variable-length types such as VARCHAR are
stored using a fixed length.
• MEMORY tables cannot contain BLOB or TEXT columns.
• MEMORY includes support for AUTO_INCREMENT columns.
• Non-TEMPORARY MEMORY tables are shared among all clients, just like any other non-TEMPORARY
table.
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