[architecture] personal understanding of Oracle segment blocks

1. Segment chunks are the logical concept of Oracle databases. The block belongs to the zone, and the area belongs to the segment.

2. When Oracle creates a table, it allocates a segment to install the table. It can be understood that a table is a segment.

3. Point 2 is not accurate enough. In fact, Oracle does not allocate logical structures when creating empty tables (to save more space) when no data is added, but only when data is added. Of course, a table is still a segment.

4. An area is made up of many consecutive blocks. When Oracle creates a table and adds data, it creates a new range, and Oracle adds data to these new extents, which are made up of many blocks. When this area is used up, the next area will be generated.

5. The size of the block is 8k by default and can be modified.

6. The Oracle database is composed of many tables, and the table is made up of many data rows.

7. There are multiple rows of data in each block, and a row of data usually can only be in one block. Because a block is 8k, a row of data must be much smaller than this value, so a block can hold a lot of data, which is enough.

8. The block is the smallest unit of Oracle Imax O. ICompo refers to the process from disk to memory. The data is stored on disk. So usually we retrieve a row of data, Oracle in the disk, it is impossible to call only a row of data, at least one block, that is, 8k. For example, I want to read a row of data size of 100 bytes, but every time Oracle reads this row of data, it will read its block, which is 8k.

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