In order for this site to work correctly, and for us to improve the site, we need to store a small file (called a cookie) on your computer.
By continuing to use this website, you agree to our cookies and privacy policy.
Home page Home page Home page Home page
Pixel Header R1 C1 Pixel
Pixel Header R2 C1 Pixel
Pixel Header R3 C1 Pixel

How Indexes Are Updated

Indexing continues to be one of the least understood areas of AREV and our subscribers repeatedly request additional clarification on related issues. Following on from our issue describing index record structures (Volume 2 Issue 1), the following documents the logic flow of the system when updating indexes.

All i/o to an indexed file must first pass through SI.MFS. When this detects that a change has been made it updates the !INDEXING file with transaction records and then as time is made available (or indexes are flushed manually), it updates the indexes and balances the BTREES. This is not achieved by one self contained AREV routine but by a whole string of routines, SI.MFS, INPUT.CHAR, INDEX.CONTROL, FILE.DISTRIBUTOR, F.DISTRIBUTOR, F.INDEXER, BTREE.READ and BTREE.WRITE. The process taken could be represented by the following Pseudo Code

0002       SI.MFS
0003         LOOP
0005         REPEAT
0006         READ RECORD 0
0007         UPDATE RECORD 0
0008         IF RECORD 0 TOO BIG THEN
0012         END
0013         UNLOCK !INDEXING,0

Note here that if somebody else on a network is involved in a record write involving several indexes, your station will appear to hang when you file a record with indexes. Your station will have to wait for the !INDEXING,0 lock.

When control is returned to INPUT.CHAR, the following occurs

0001       INPUT.CHAR
0002         LOOP
0004         REPEAT

Note here that if there is a replace background process specified in the environment (2.X only), this will be called in place of INDEX.CONTROL and no further processing will take place. References to Post Index Check following also only apply in 2.X.

0001       INDEX.CONTROL
0002            LOOP
0003              IF NOT KEY STROKE THEN
0004                 CALL FILE.DISTRIBUTOR
0005                 FILE.DISTRIBUTOR
0006                   LOOP
0007                   UNTIL KEY STROKE
0008                      MOVE RECORDS FROM !INDEXING TO !FILE
0009                   REPEAT
0010              END
0011              IF NOT KEY STROKE THEN
0012                 CALL F.DISTRIBUTOR
0013                 F.DISTRIBUTOR
0014                   LOOP
0015                   UNTIL KEY STROKES
0017                   REPEAT
0018              END
0019              IF NOT KEY STROKE THEN
0020                 CALL F.INDEXER
0021                 F.INDEXER
0022                   LOOP
0023                   UNTIL KEY STROKES
0024                      UPDATE BTREE NODES
0025                   REPEAT
0026              END
0028              END
0029            UNTIL KEY STROKE
0030            REPEAT
0031            RETURN TO INPUT CHAR

Note that these stages can be interrupted at any stage by pressing a key. The process of performing the BTREE update incrementally slows the system down but permits it to be done with minimal interference with normal work.

(Volume 2, Issue 9, Pages 5,6)
Pixel Footer R1 C1 Pixel