Bind to Finish

1
Bind to Finish
UKIUA Roadshow April 2004

• Steve Roberts Acebyte Ltd
• www.acebyteltd.demon.co.uk

2
Abstract

• This session provides an overview of the
  processes
• involved in processing a run unit from a bind
• through to a finish. It examines the components
  used
• by the application and the DBMS when processing
• requests for data, looking at the breakdown of a
• Bind Run Unit, Bind Record and subsequent DML
• processing through to a finish.

3
Content

• Application Components
• DBMS Components
• Access
• Binds
• DML Data Movement
• Finish

4
Content

• Application Components

5
Application - Components

• Subschema Components
• Subschema name
• Record, Set Area Names
• Record Definitions
• Subschema Control
• DML
• IDMS Interface Modules

6
Subschema Components
01 SUBSCHEMA-SSNAME PIC X(8) VALUE
CUSTSS01 01 SUBSCHEMA-RECNAMES. 03
SR1054 PIC X(16) VALUE CUSTOMER. 03
SR1055 PIC X(16) VALUE ACCOUNT. 01 SUBSCHEMA-S
ETNAMES. 03 CUST-ACCT PIC X(16) VALUE
CUST-ACCT. 01 SUBSCHEMA-AREANAMES. 03
CUST-AREA PIC X(16) VALUE CUST-AREA. 03
ACCT-AREA PIC X(16) VALUE ACCT-AREA.
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Record Definitions
01 CUSTOMER. 03 CUST-ID PIC X(16). . . 01 ACC
OUNT. 03 ACCT-ID PIC 9(16). . .
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Subschema Control
01 SUBSCHEMA-CTRL. 03 PROGRAM-NAME PIC
X(8) VALUE SPACES. 03 ERROR-STATUS PIC
X(4) VALUE 1400. 03 DBKEY PIC S9(8) USAGE
COMP SYNC. 03 RECORD-NAME PIC X(16) VALUE
SPACES. 03 AREA-NAME PIC X(16) VALUE
SPACES. 03 ERROR-SET PIC X(16) VALUE
SPACES. 03 ERROR-RECORD PIC X(16) VALUE
SPACES. 03 ERROR-AREA PIC X(16) VALUE
SPACES. 03 IDBMSCOM-AREA PIC X(100) VALUE
LOW-VALUE. 03 IDBMSCOM REDEFINES
IDBMSCOM-AREA PIC X OCCURS 100. 03 DIRECT-DBK
EY PIC S9(8) USAGE COMP SYNC. 03 DML-SEQUENCE PIC
S9(8) USAGE COMP SYNC.
9
DML

• BINDS
• Run Unit
• Records
• Data Manipulation
• Find/Get/Obtain
• Store/Modify/Erase
• Connect/Disconnect
• Recovery Control
• Commit/Finish/Rollback

10
IDMS Interface Modules

• IDMSL Pre 12.0 IDMS (Pre 12.0)
• IDMSINTB IDMSB102
• IDMS
• IDMSNCLI
• CICS Interface Modules
• IDMSCINT
• IDMSINTC
• IDMSINTL

11
IDMS IDML

• 12.0 and above IDMS module calls IDMSNCLI (Native
  Client)
• IDML and pre 12.0 IDMS modules call IDMSINTB
• INTB tries to load IDMSB102
• If found INTB processes the request
• If not found INTB calls IDMSNCLI to process
  request
• Processing is similar in CICS using INTC INTL

12
IDMS IDML

• IDML Pre 12.0 IDMS
• When using the IDML or pre 12.0 IDMS batch
  interface,
• a copy of the applications SSC is stored in an
  MVS
• CSA paket at each request. On the CV side the
  contents
• are copied to an expanded version of SSC used by
  CV
• IDMS
• When using the now standard IDMS batch
  interface
• SSC is not copied into the paket. The interface
  (NCLI)
• stores specific data from SSC into a parameter
  block
• (CPS) into the paket. On the CV side the request
  is rebuilt
• from these parameters and SSC updated.

13
Expanded DML

• IDMS Pre-compiler expands DML
• Expanded DML has standard format
• Expands to call to IDMS module
• Passes Parameter List to IDMS module
• 1st Parameter is always address of SSC
• 2nd Parameter is an address within IDBMSCOM
• Nth Parameters dependent on function
• IDMS module stores parameters in SSC

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Expanded DML - Examples
OBTAIN FIRST CUSTOMER WITHIN CUST-AREA. MOVE
0005 TO DML-SEQUENCE CALL IDMS USING
SUBSCHEMA-CTRL IDBMSCOM(19)
SR1054 CUST-AREA IDBMSCOM(43).
OBTAIN NEXT ACCOUNT WITHIN CUST-ACCT. MOVE
0006 TO DML-SEQUENCE CALL IDMS USING
SUBSCHEMA-CTRL IDBMSCOM(10)
SR1055 CUST-ACCT IDBMSCOM(43).
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Content

• Application Components

• DBMS Components

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DBMS - Components

• Subschema Control (Expanded Version)
• IDMSNSRV / IDMSDBMS / IDMSDBIO
• Subschema Load Module
• Run Unit (TBK/VB50 VIB)
• DMCL / DBNAME Table
• DB Buffers
• JNL Buffers

17
DBMS Components

• IDMSNSRV
• Takes the request passed and passes the
  parameters to IDMSDBMS using the VB50
• On completion of a request NSRV updates the SSC
  block with status information from the VB50
• NSRV works with the expanded SSC

18
Content

• Application Components

• DBMS Components

• Access

19
Access - Local

• Local Access
• Refers to the fact that the application code
  issuing the DML is in the same address space as
  the DBMS itself, this includes -
• Local Mode Batch
• DC Tasks
• UCF Tasks
• UCF access is local because the application runs
  in the CV address space. However, UCF is really
  remote access as it uses the same ESE/ERE/PAKET
  mechanism (described later) to pass 3270
  Datastreams (terminal data) NOT records

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Local Mode Batch DC/UCF Tasks

• Application and DBMS are in the same address
  space
• Application SSC and DBMS SSC are in the same
  address space
• Bind address is address of record in application
  W-Storage
• Record data is read and written to and from the
  DB buffers to application W-Storage

21
Access - Local
IDMS
IDMS
VB50 (Run Unit)
22
Access - Remote

• Remote Access
• Refers to the fact that the application code
  issuing the DML is in a different address space
  to the DBMS, this includes -
• CV Mode Batch
• CICS
• UCF
• As indicated before UCF in remote access terms is
  used to run a local access task. The remote
  access route is used to pass screen data and NOT
  record data

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CV Mode Batch CICS

• Application and DBMS are in separate A/S
• Application SSC is in Application A/S
• DBMS SSC in CV A/S
• CSA Paket used to pass requests between A/Ss
• SSC or Equivalent passed via Paket
• Record Data Passed via Paket
• Record Bind Address
• Bind address stored in Bind Address Table in
  Paket
• All DBMS Records have bind Address set to
  address of record buffer in Paket

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Access - Remote
Batch Address Space
CV Address Space
Batch ERUS
CICS ERUS
Application W-Stor DML
IDMS
IDMS
IDMS
IDMS
IDMS
CICS Address Space
IDMSDBMS
IDMSDBIO
DMCL
Subschema(s)
CINT
VB50 (Run Unit)
VB50 (Run Unit)
DB Buffers
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IDMS IDML

• IDMSNCLI
• Determines function from application SSC
• Builds request block
• Passes it via Paket
• Calls IDMSCONN to process SYSIDMS
• CV builds DBMS SSC from request block
• IDMSINTB
• Passes SSC as is in Paket
• CV copies passed SSC to DBMSs SSC

26
CV Access

• At startup CV allocates in MVS CSA
• 1 ESE (External Services Element)
• n EREs (External Request Elements)
• Stores ESE address in IDMS SVC table
• Writes SVC Number and CV number to SYSCTL file
• This allows Batch and CICS to access CV

27
Content

• Application Components

• DBMS Components

• Access

• Binds

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Binds

• Bind Run Unit
• Establishes communication with DBMS and creates
  the run unit
• Allocates TBK VB50 to represent run unit
• Resolves the logical subschema load module with
  the physical database
• Subschema name must be present
• DBName is optional

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Binds

• The bind run unit causes the DBMS to resolve the
  logical subschema with the physical DMCL using
  the DBNAME table
• At this point in the run unit the DBMS does not
  known which areas will be used
• It therefore has to resolve all areas it finds in
  the subschema

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Binds

• Bind Record
• Establishes addressability for each record the
  application may use
• Bind address stored in VB50 record control block
• For Local Access bind address will be address of
  the record in applications w-storage
• For Remote Access bind address will be the
  address of the paket record buffer

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CV Access Bind Run Unit

• When a Bind Run Unit is issued from a Batch job
  it will attempt to open the SYSCTL file
• If found it will attempt to communicate with CV
• If not found will load DBMS modules and run in
  local mode
• CICS Tasks issuing Bind Run Unit will either open
  a SYSCTL or have the CV information linked into
  the IDMSINTC module

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CV Access Bind Run Unit

• Gets SVC and CV from SYSCTL
• Issues SVC call to SVC to signon to CV
• SVC code locates the ESE and allocates an
  available ERE and Paket
• Posts ESEECB
• Application waits on ECB in its own address space
  (LREECB)

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CV Access Bind Run Unit

• CV will allocate a task to represent the external
  run unit
• Allocate SSC
• Locate (or load) the subschema module
• Allocate TBX/VB50 control blocks to represent the
  run unit
• A BGIN record is built.
• If sysgen nojournal retrieval is set the BGIN is
  not written to the journal until the run unit
  actually performs an update.

34
CV Access Bind Run Unit

• Issues SVC to indicate request complete
• CV Task waits on EREECB
• SVC will post LREECB to indicate request
  completed
• Interface (IDMSINTB or IDMSNCLI) copies or
  updates applications SSC from the Paket
• Passes control back to applications code

35
CV Access
App A/S
Working Storage 01 CUSTOMER . 01 ACCOUNT . . SSC
MVS CSA
SYSCTL
Paket
SCV 211 CV 56
SSC / CPS BAT Buffer
36
BIND Record

• DBMS needs to know where to read and write record
  content.
• Bind record passes the address of the record in
  applications working storage
• Local Batch and DC Mode Task
• Actual record address is stored in VSR51
• CV Batch CICS
• Actual record address is stored in Bind Address
  Table in the paket
• All record VSR51s hold the same paket record
  buffer address

37
Bind Address

• IDMSDBMS itself does not care where the bind
  address is. IDMSDBMS simply moves the data to or
  from the DB page to or from the record bind
  address stored in the VB50 VSR51 control block.
• For local access the data is read/written
  directly to the applications working storage
• For remote access
• DBMS reads/write data to/from the paket buffer
• the interface modules on the application side
  move the data to or from the paket buffer to or
  from the application working storage using the
  bind address stored in the paket Bind Address
  Table

38
Bind Address

• When IDMSDBMS stores the bind address in the
  VSR51 it also calculates the bind address of each
  key in the record (i.e. Calckey, sortkey,
  indexkey) and stores it in another VB50 control
  block VCR55
• This allows IDMSDBMS to address key fields within
  the record

39
SUPABIND

• For remote access, all the VB50 record control
  blocks (VSR51) will contain the same bind address
  the address of the paket buffer
• Therefore, a remote bind record request does not
  actually do anything on the CV side, it only
  stores the records address in the paket BAT
• On the first functional call (non Bind Record),
  DBMS checks the BAT. Those records for which a
  bind has been issued it will bind all those
  records to the paket record buffer address

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Content

• Application Components

• DBMS Components

• Access

• Binds

• DML Data Movement

41
DML Data Movement

• Once the run unit has been established each DML
  is passed through from the application to DBMS to
  process
• The request on the CV side is stored in the Run
  Unit control block VB50
• IDMSDBMS interprets the request in the VB50 and
  processes the request calling IDMSDBIO, Lock
  management and Journal Management as and when
  required

42
DML Data Movement

• Local Access
• The request is passed through to the VB50 for
  IDMSDBMS to process
• If record data needs to be read or written to or
  from the application, IDMSDBMS uses the records
  bind address, which will be in the actual
  applications W-storage.
• IDMSDBMS doesnt care where the bind address
  actually is, it simply uses the address it finds
  in it VB50 record control block

43
Data Movement

• Remote Access Application Side
• The request is passed into the paket (SSC or CPS
  depending on interface used)
• The record data from application w-storage is
  stored into the paket record buffer
• Issues SVC call to post EREECB
• Application A/S waits on ECB pointed to by the
  ERE (usually refered to as LREECB)

44
Data Movement

• Remote Access CV side
• The task established at bind run unit time is
  waiting on EREECB. As we have just seen that ECB
  has just been posted, so the task is eligible to
  run
• The task will update the CV side copy of SSC from
  the paket SSC or CPS and re-build the parameter
  list into the VB50 for IDMSDBMS to process

45
Data Movement

• Remote Access CV Side
• IDMSDBMS works in same way as it would for local
  access
• It determines the request from the VB50
  parameters
• If it needs to read or write record data it uses
  the bind address from the VSR51, it just so
  happens that the address in this case is in the
  paket, again IDMSDBMS doesnt care where the bind
  address is

46
Data Movement

• Remote Access CV Side
• When the request is complete, the CV interface
  modules will update the paket SSC or CPS from the
  CV copy of SSC
• It will issue an SVC call to post the ECB
  pointed to by the ERE (LREECB) to indicate
  request is complete
• CV Task waits on EREECB

47
Data movement

• Remote Access Application Side
• The application was waiting on LREECB which has
  been posted
• The application interface modules either copy
  paket SSC to application SSC or update
  application SSC from the paket CPS
• Copies record data from paket record buffer to
  application w-storage using records bind address
  in the paket BAT
• Control is then passed back to the application
  code itself

48
Data Movement
App A/S
MVS CSA
CV A/S
Working Storage 01 CUSTOMER . 01 ACCOUNT . .
Tasks TCE TCE
ESE ERE ERE ERE ERE
VB50 VSR51 (CUSTOMER) Paket Buffer Addr VSR51
(ACCOUNT) Paket Buffer Addr
Database
Paket
BAT CUSTOMER ADDR ACCOUNT ADDR SSC . . BUFFER

DB Buffer Page Page Page
49
Data Retrieval

• Obtain Calc Customer
• IDMSDBMS
• Determines the function from VB50
• 1st Parm Address of SSC
• 2nd Parm Address of offset within SSC
• Sets major code 03 in error status
• 3rd Parm for Obtain Calc
• address of field which holds the record name
• i.e. address points to the literal CUSTOMER

50
Data Retrieval

• Obtain Calc Customer
• IDMSDBMS
• Using the Record Name
• Locates Record in Subschema
• Area Name Records page range
• Record ID
• Record length
• Prefix Length
• Address of Calc Key

51
Data Retrieval

• Obtain Calc Customer
• IDMSDBMS
• Reads the calckey
• Calls IDMSCALC passing
• Records page range
• Calckey value
• IDMSCALC passes back the target page number

52
Data Retrieval

• Obtain Calc Customer
• IDMSDBMS
• Calls DBIO for the Target Page
• Walks Calc Chain looking for match
• Record ID
• Calckey
• If not found
• Sets 26 minor code in error status
• Passes control back to caller

53
Data Retrieval

• Obtain Calc Customer
• If record is found IDMSDBMS
• Moves the data portion from the database page to
  the records bind address
• Updates currency
• Sets 0000 error status
• Passes control back to caller

54
Data Retrieval

• Obtain Calc Customer
• If the record is fragmented or compressed then
  IDMSDBMS first constructs the record in the VB50
  record buffer
• It then moves the record from the VB50 record
  buffer to the bind address

55
Data Update

• Store Customer
• IDMSDBMS
• Determines the function from VB50
• 1st Parm Address of SSC
• 2nd Parm Address of offset within SSC
• Sets major code 12 in error status
• 3rd Parm for Store
• address of field which holds the record name
• i.e. address points to the literal CUSTOMER

56
Data Update

• Store Customer
• IDMSDBMS
• Using the Record Name
• Locates Record in Subschema
• Storage Mode
• Area Name Records page range
• Record ID
• Record length
• Prefix Length
• Address of Calc Key

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Data Update

• Store Customer
• IDMSDBMS
• Reads the calckey
• Calls IDMSCALC passing
• Records page range
• Calckey value
• IDMSCALC passes back the target page number

58
Data Update

• Store Customer
• IDMSDBMS
• Calls DBIO for the Target Page
• Locates Space for the record
• Sets minor code 11 if cannot find space
• Writes null BFOR image to journal buffer
• Moves the data from the bind address to the page
• Writes AFTR image to journal buffer

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Data Update

• Store Customer
• IDMSDBMS
• Builds Prefix Portion
• Using set currencies determines set position for
  each automatic set (including Calc set)
• Connects record into set
• Any sets which have manual connection are set to
  high values
• Any set in which it is the owner, it stores the
  dbkey of the record itself (empty set)
• Writes prefix BFOR / AFTR image for each record
  affected by set connections

60
Data Update

• Store Customer
• IDMSDBMS
• Updates currencies
• Sets error-status to 0000
• Passes control back to caller
• The update itself is not necessarily written at
  this stage to the physical file, the update is
  only to the DB buffer

61
Update

• When an update DML is processed one or more DB
  buffers will be updated
• Each DB buffer is represented by a control block
  called a BME
• Each BME has
• Address of its Buffer
• Page number
• Must Write Switch
• VB50 List
• Journal Sequence Number

62
Update

• When a page is updated in a buffer
• Must write switch (MWS) is set on
• VB50 address of run unit is stored
• Up to three run units can update a page in a
  buffer

63
Update

• If the updated buffer is selected to read another
  page
• MWS indicates the page currently in the buffer
  must be written first
• DBIO is called to write the page out
• DBIO first checks that journal images are written
• Then issues an I/O to write the page
• This is known as a forced write
• When complete the MWS is set off and VB50 list is
  cleared
• New page is read into the buffer

64
Update

• The VB50 also contains a bit map which represents
  all of the DB buffers in the DMCL
• When the run unit updates a buffer the bit
  representing the buffer is set on
• The MWS, VB50 address and this buffer bit map are
  important to what happens at commit or finish
  processing

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Content

• Application Components

• DBMS Components

• Access

• Binds

• DML Data Movement

• Finish

66
Finish

• Finish processing is basically a commit process
  followed by a termination process which deletes
  the run unit control blocks and terminates
  communication with the DBMS
• Commit processing ensures that any updates made
  by the run unit are physically written to the
  database and ensures that those updates are
  journalled correctly

67
Finish

• Commit Processing has to
• Find the buffers updated by the Run Unit
• Checks if those buffers contain updates for the
  run unit
• Call DBIO to write the updated page
• DBIO will ensure any journal images for the
  updates have been written
• DBIO will issues an I/O to write the page
• Write an ENDJ (or COMT for a commit command) to
  the journal to signal completion of a recovery
  unit

68
Finish

• Find Buffers Updated by the Run Unit
• VB50 has buffer bit map
• Each bit set on represents a buffer updated by
  the run unit
• Checks BME for each buffer updated

69
Finish

• Check if buffer contains updates for the run unit
• Update has already been written if either
• MWS is off
• MWS is on BME does not hold run units VB50
  address
• Update has NOT been written if
• MWS is on BME has rununits VB50 address
• When this is the case DBIO is called to write the
  page

70
Finish

• Calls DBIO to write the page
• DBIO ensures any journal images for the updates
  to the page have been written
• The BME also holds the last journal sequence
  number of the last update performed on the page
• Each Journal Buffer Element (JBE) holds the
  highest journal sequence number for journal
  images in its buffer
• DBIO checks for any JBEs with a highest sequence
  number lower or equal to the sequence number held
  in the buffers BME.
• Any JBE found, its journal buffer must be written
  before the DB page is written

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Finish

• Calls DBIO to write the page
• Issues I/O to write the page to the physical file
• Continues to check next buffer until all buffers
  updated by the run unit have been checked and
  written if needed

72
Finish

• Writes to the journal to signal completion of
  recovery unit
• For a FINISH writes an ENDJ to journal buffer
• For a COMMIT writes a COMT to journal buffer
• Issue I/O to write journal buffer
• When I/O completes control passed by to
  application

73
Content

• Application Components

• DBMS Components

• Access

• Binds

• DML Data Movement

• Finish

74
Questions
?