Relational DB in-memory?

sql redis relational in-memory
ilupper picture ilupper · Mar 16, 2011 · Viewed 7.6k times · Source

I have a simpleton question on Redis. If the key to it's performance is that it's in-memory, whey can't that be done on a regular SQL db?

Answer

user166390 picture user166390 · Mar 16, 2011

Any DBMS can be run "in memory". Consider the use of a ramdisk. However, most DBMSs (those with SQL) are not designed to run entirely in memory and put alot of effort to minimize disk IO and paging: a DBMS works very hard to keep the "relevant data" hot (in memory and in cache) -- IO is slow, slow slow.

This is because database data is often [and has historically been] significantly larger than main memory. That and main-memory is volatile :-) [ACID DBMSs do lots of works with write-ahead logging -- to a non-volatile store -- and other techniques to ensure data is never corrupted, even in case of a unexpected shutdown.]

Some databases, like SQLite use the same format for the disk and memory stores even though they explicitly support an in-memory store. Support for other [in-memory] back-ends and memory usage tuning vary by provider.

Happy coding.

Related questions

How do I UPDATE from a SELECT in SQL Server?

In SQL Server, it is possible to insert rows into a table with an INSERT.. SELECT statement: INSERT INTO Table (col1, col2, col3) SELECT col1, col2, col3 FROM other_table WHERE sql = 'cool' Is it also possible to update a …

Read More
How do I perform an IF...THEN in an SQL SELECT?

How do I perform an IF...THEN in an SQL SELECT statement? For example: SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product

Read More
How do I import an SQL file using the command line in MySQL?

I have a .sql file with an export from phpMyAdmin. I want to import it into a different server using the command line. I have a Windows Server 2008 R2 installation. I placed the .sql file on the C drive, and …

Read More