|
Programming Interface Information:
This information is NOT
intended to be
used as Programming Interfaces of VM/ESA. It is to be used for diagnosis only. |
CNODE
Cross Reference (Contains links to field and bit definitions)
CNODE Prolog
Name : HCPCNODE
Description: Collision node for MDC hash table.
DSECT : CNODE
Function : To provide mapping of a MDC overflow hash
table node.
Created by : HCPFTHRD
Deleted by : HCPFTHUD, HCPFTHDC, HCPFTUFL, HCPFTURM
Notes :
The MDC hash table is comprised of a base hash table and
collision page(s). A hashing algorithm is used to convert
a key to the address of a base node. The base node is 3
words and is either empty or holds a single TCHBK (see
HCPTCHBK).
Multiple keys can hash to the same base node and such
collisions are handled via a chaining scheme that links
the base node with additional (collision) nodes that lie
outside the hash table proper. The second word of the
last (or only) TCHBK in the chain contains data relating
to the track represented by that TCHBK. The second word
of all other TCHBKs contain the address of a collision
node with the high-order bit set to one to indicate that
there are additional nodes. (The data words never have
the high-order bit set to one.)
A collision node is comprised of a TCHBK prefixed by a
fullword containing the data that was displaced from the
preceding TCHBK to make room for a forward pointer.
Base Node (in hash table)
+------------+------------+------------+
| TCHBK |
+------------+-----+------+------------+
|
+------------------+
|
v Collision Node (in collision page)
+------------+------------+------------+------------+
| N-1 data | TCHBK |
+------------+------------+------+-----+------------+
|
+--------------------------------+
|
v Terminal Collision Node (in collision page)
+------------+------------+------------+------------+
| N-1 data | TCHBK |
+------------+------------+------------+------------+
CNODE Control Block Content
CNODE DSECT
Hex Dec Type/Val Lng Label (dup) Comments ---- ---- --------- ---- -------------- -------- 0000 0 Structure CNODE Collision node for MDC hash table. 0000 0 Address 4 CNONXTAV (0) Address of next collision node if on available chain Zero => end of chain 0000 0 Signed 4 CNOPREV Data for previous entry 0004 4 Bitstring 12 CNOTCHBK (0) TCHBK in collision node The remainder of this DSECT maps the TCHBK that resides in the collision node. For details see HCPTCHBK COPY. 0004 4 Signed 4 CNOKEY Hash key 0008 8 Address 4 CNOTKFMT The hash data/pointer **TCHCOLFG EQU PFX8000S Flag to indicate CNOCDATA is a collision pointer. Marks the TCHENTRY inside the collision node as format 'b' 000C 12 Address 4 CNOCPEBK (0) CPEBK address High order bit of CNOCPEBK determines if unconditional delete is required. TCHUDREQ is that bit's name. Note that if this bit is on, the remainder of CNOCPEBK may be zero. I.E. only an unconditional delete is deferred. 000C 12 Address 4 CNOADRLX (0) Virtual address etc 000C 12 Bitstring 1 CNOORIG (2) SSSP of virtual address 000E 14 Bitstring 1 CNOLOCK Lock nibble is right half, final P of vaddr in left 000F 15 Bitstring 1 CNOTBENT Flags and Table index 0000075C CNOBCKUP PFX4 Distance to back up from the beginning of a TCHBK to the beginning of a CNODE This is length of CNOPDATA 00000010 CNOCSIZB *-CNODE Size of collision entry
CNODE Storage Layout
*** CNODE - Collision node for MDC hash table. * * +---------------------------+---------------------------+ * 0 | CNOPREV | CNOKEY | * +---------------------------+-------------+------+------+ * 8 | CNOTKFMT | CNOORIG |:LOCK |:TBENT| * +---------------------------+-------------+------+------+ * 10 * *** CNODE - Collision node for MDC hash table.
CNODE Cross Reference
(contains links to field and bit definitions)Symbol Dspl Value -------------- ---- -----CNOADRLX 000C
CNOBCKUP 000F 0000075C
CNOCPEBK 000C
CNOCSIZB 000F 00000010
CNOKEY 0004
CNOLOCK 000E
CNONXTAV 0000
CNOORIG 000C
CNOPREV 0000
CNOTBENT 000F
CNOTCHBK 0004
CNOTKFMT 0008
Last updated on 3 Aug 1999 at 11:46:07 EDT.
Copyright IBM Corporation, 1990, 1999