Table E (File architecture)

Holds Large Object Data (BLOBs and CLOBs)

Enabled by reorganizing / CREATEing a file with ESIZE greater than 0, and then defining a field with a data type of CLOB or BLOB (the file must have an ESIZE for the latter to occur).

Available as of Model 204 V7.1

Summary

Storage and manipulation of Large Objects (LOBs) differs greatly depending on whether FILEORG x'100' is set.

Table E without FILEORG x'100'

Table E with FILEORG x'100'

Regardless of the FILEORG setting, an individual LOB occurrence may be up to 2 Gb. The maximum size of Table E is 1,073,741,823 pages.

Table E Differences Without / With the x'100' Setting

Function	non x'100'	x'100'
General space management	LOBs require contiguous space New LOBs are always written starting at EHIGHPG; if ESIZE is reached, Table E is scanned for contiguous space (due to deletes). Table E can 'fill' even with many available pages if the space is fragmented.	LOBs are stored as a series of chained pages, and new LOBs are written first using those in the reuse queue (due to deletes). Table E will 'fill' only if all pages are used.
Overhead	There is a 27 byte pointer in the record on Table B / X for every occurrence of every LOB or 30 a byte pointer if the field is not pre-allocated There are bitmap pages for every 49152 pages in Table E (plus 16 additional overhead pages) The first page of every LOB occurrence contains a 32 byte LOB header.	There is a 27 byte pointer in the record on Table B / X for every occurrence of every LOB There are 4 bytes reserved on every page in Table E for the chaining of LOBs.
Storing small amounts of data in a LOB field	Even a single byte of data requires a full page of Table E	Fields may be defined with the MINLOBE attribute to permit small (MINLOBE may be set up to 200 bytes) of data to be stored directly in the record in Table B. But see the 'Change' section, below.
Change a LOB	At the time a LOB is first stored, if you expect to subsequently need to increase its size, you will need to RESERVE the necessary space in the initial add.	LOBs may be changed as needed (on adds and stores, the RESERVE, if present, is ignored). Change statements are not permitted if MINLOBE is in use. (A delete / add or insert may be used).
COMPACTE command	Is used to defragment Table E to increase the amount of contiguous space.	The COMPACTE command is not necessary, and attempts to execute it will generate an error.