How does QD respond to ad hoc analytical read-only complex queries faster than a standard RDBMS on a PC?
First, QD ensures that only those columns that are included in the query criteria will be retrieved from the disk in order for the query engine to compute the result set. The remaining row columns (i.e. those not included in the query criteria) are left alone. Retrieving only those columns that are necessary allows more data to be packed into fewer read operations, hence the greater query speed. Second, by compressing its data, the QDB can squeeze more data on a single page and then read it out faster. In any computer system, the disk is the performance bottleneck, as disk reads can be thousands of times slower than memory reads. A compressed database requires fewer read operations than an uncompressed one to retrieve its data. Because the data is compressed, transfers from disk to memory are faster and more data can be placed in cache memory. Data operations to memory are many hundreds of times faster than disk I/O operations. Since QD is read-only, no locking, logging, or other opera
