Database Reference
In-Depth Information
ON-DISK aND MeMOrY-OptIMIZeD taBLeS: DIFFereNt
StOraGe CONCeptS
there is a conceptual difference in how on-disk and memory-optimized data are stored. On-disk tables store the
single, most recent version of the row. Multiple updates of the data row change the same row object multiple
times. Deletion of the row removes it from the database. Finally, it is always possible to locate a data row in a
data file when needed.
On the other hand, memory-optimized files store multiple versions of the row. Multiple updates of the data row
generate multiple row objects, each of them having a different lifetime. It is impossible to predict where a data
row is stored in the files. nor are there use-cases for such an operation. the purpose of data and delta files is to
provide data durability and improve the performance of loading data into memory on database startup.
Figure
32-24
provides a high-level overview of the information stored in checkpoint files.
Figure 32-24.
Data in checkpoint files
Figure
32-25
shows an example of a database with four pairs of data and delta files. The vertical rectangles with a
solid fill represent data files. The rectangles with a dotted fill represent delta files.
