Blobspace Page Types

Every blobspace chunk contains three types of pages:
  • A blobspace free-map page
  • A bitmap page
  • Blobpages

Blobspace Free-Map Page

The blobspace free-map page identifies unused blobpages so that the database server can allocate them as part of simple-large-object creation. When a blobpage is allocated, the free-map entry for that page is updated. All entries for a single simple large object are linked.

A blobspace free-map page is the size of one database server page. Each entry on a free-map page is 8 bytes, stored as two 32-bit words, as follows:
  • The first bit in the first word specifies whether the blobpage is free or used.
  • The next 31 bits in the first word identify the logical-log file that was current when this blobpage was written. (This information is needed for logging TEXT or BYTE data.)
  • The second word contains the tblspace number associated with the simple large object stored on this page.

The number of entries that can fit on a free-map page depends on the page size of your computer. The number of free-map pages in a blobspace chunk depends on the number of blobpages in the chunk.

Blobspace Bitmap Page

The blobspace bitmap page tracks the fullness and number of blobspace free-map pages in the chunk. Each blobspace bitmap page is capable of tracking a quantity of free-map pages. The size of the blobspace bitmap page depends on the size of the system page. If the system page is 2K, the blobspace bitmap page can track 2,032,128 blobpages. If the system page is 4K, the blobspace bitmap page can track 8,258,048 blobpages.

Blobpage

The blobpage contains the TEXT or BYTE data. Blobpage size is specified by the database server administrator who creates the blobspace. Blobpage size is specified as a multiple of the page size.