This topic describes the heap table structure of PolarDB for PostgreSQL(Compatible with Oracle).
Item | Description |
---|---|
table files | A table file that consists of one or more data files. The number of data files depends on the data file size. If the data file size exceeds 1 GB, a new data file is generated. |
file | A data file that consists of multiple data blocks. |
page | A data block that consists of multiple rows. |
page header | The data block header. For more information, see Information about the data block header. |
tuple | A row. |
tuple header | The row header. For more information, see Information about the row header. |
Field | Description |
---|---|
pd_lsn | The position where the write-ahead logging (WAL) file of the data block is modified for the last time. |
pd_checksum | The page checksum. |
pd_flags | The flag bits. |
pd_lower | The offset to the start of free space. |
pd_upper | The offset to the end of free space. |
pd_special | The offset to the start of special space. |
pd_pagesize_version | The page size and the layout version number. |
pd_prune_xid | The earliest XMAX that is not deleted from the page. If none exists, the value is 0. |
Field | Description |
---|---|
t_xmin | The insert transaction identifier (XID). |
t_xmax | The delete XID. |
t_cid | The command identifier (CID) of the command that you run to insert or delete data. |
t_ctid | The tuple identifier (TID) of the current row version or later. |
t_infomask | The flag bits. |
t_infomask2 | The extra flag bits. |
t_hoff | The offset to user data. |
tuple data | The actual data. |