Database lock considerations

Listed here are the commonly used database functions and the types of locks they place on database files.

Table 1 summarizes some of the most commonly used database functions and the types of locks they place on database files. The types of locks are explained on the next page.

Table 1. Database functions and locks
Function	Command	File Lock	Member/Data Lock	Access Path Lock
Add Member	ADDPFM, ADDLFM	*EXCLRD		*EXCLRD
Change File Attributes	CHGPF, CHGLF	*EXCL	*EXCLRD	*EXCLRD
Change Member Attributes	CHGPFM, CHGLFM	*SHRRD	*EXCLRD
Change Object Owner	CHGOBJOWN	*EXCL
Check Object	CHKOBJ	*SHRNUPD
Clear Physical File Member	CLRPFM	*SHRRD	*EXCLRD³
Create Duplicate Object	CRTDUPOBJ	EXCL (new object) SHRNUPD (object)
Create File	CRTPF, CRTLF, CRTSRCPF	*EXCL
Delete File	DLTF	*EXCL		*EXCLRD
Grant/Revoke Authority	GRTOBJAUT, RVKOBJAUT	*EXCL
Initialize Physical File Member	INZPFM	*SHRRD	*EXCLRD
Move Object	MOVOBJ	*EXCL
Open File	OPNDBF, OPNQRYF	*SHRRD	*SHRRD	*EXCLRD
Rebuild Access Path	EDTRBDAP, OPNDBF	*SHRRD	*SHRRD	*EXCLRD
Remove Member	RMVM	*EXCLRD	*EXCL	*EXCLRD
Rename File	RNMOBJ	*EXCL	*EXCL	*EXCL
Rename Member	RNMM	*EXCLRD	*EXCL	*EXCL
Reorganize Physical File Member	RGZPFM	*SHRRD	*EXCL⁴
Restore File	RSTLIB, RSTOBJ	*EXCL
Save File	SAVLIB, SAVOBJ, SAVCHGOBJ	*SHRNUPD¹	*SHRNUPD²
¹ For save-while-active, the file lock is SHRUPD initially, and then the lock is reduced to SHRRD. See the Backup and Recovery for a description of save-while-active locks for the save commands. ² For save-while-active, the member/data lock is SHRRD. ³ The clear operation does not happen if the member is open in this process or in any other process. ⁴ If ALWCANCEL(YES) is specified, the LOCK keyword can specify a SHRUPD or EXCLRD lock instead.

The following table shows the valid lock combinations:

Lock	*EXCLRD	*SHRUPD	*SHRNUPD	*SHRRD
*EXCL¹
*EXCLRD²				X
*SHRUPD³		X		X
*SHRNUPD⁴			X	X
*SHRRD⁵	X	X	X	X
¹ Exclusive lock (EXCL). The object is allocated for the exclusive use of the requesting job; no other job can use the object. ² Exclusive lock, allow read (EXCLRD). The object is allocated to the job that requested it, but other jobs can read the object. ³ Shared lock, allow read and update (SHRUPD). The object can be shared either for read or change with other jobs. ⁴ Shared lock, read only (SHRNUPD). The object can be shared for read with other jobs. ⁵ Shared lock (*SHRRD). The object can be shared with another job if the job does not request exclusive use of the object.

Table 2 shows database locking for constraints of a database file, depending on whether the constraint is associated with the parent file (PAR) or the dependent file (DEP).

Table 2. Database constraint locks. The numbers in parentheses refer to the notes at the end of the table.
Type of function	File type	File⁵	Member⁵	Other file	Other member
ADDPFM¹	DEP	*EXCL	*EXCL	*EXCL	*EXCL
ADDPFM¹	PAR	*EXCL	*EXCL	*EXCL	*EXCL
ADDPFCST⁷	*REFCST	*EXCL	*EXCL	*EXCL	*EXCL
ADDPFCST⁶	UNQCST PRIKEY	*EXCL	*EXCL	*EXCL	*EXCL
ADDPFCST	UNIQUE PRIKEY	*EXCL	*EXCL
RMVM²	DEP	*EXCL	*EXCL	*EXCL	*EXCL
RMVM²	PAR	*EXCL	*EXCL	*EXCL	*EXCL
DLTF³	DEP	*EXCL	*EXCL	*EXCL	*EXCL
DLTF³	PAR	*EXCL	*EXCL	*EXCL	*EXCL
RMVPFCST⁷	*REFCST	*EXCL	*EXCL	*EXCL⁴	*EXCL
RMVPFCST⁶	UNQCST PRIKEY	*EXCL	*EXCL	*EXCL	*EXCL
RMVPFCST	UNIQUE PRIKEY	*EXCL	*EXCL
CHGPFCST		*EXCL	*EXCL	*SHRRD	*EXCL
¹ If adding a physical file member causes a referential constraint to be established. ² If removing a physical file member causes an established referential constraint to become defined. ³ When deleting a dependent or parent file that has constraints established or defined for the file. ⁴ When the Remove Physical File Constraint (RMVPFCST) command is invoked for the parent file which has constraints established or defined, the parent and any logical files over the parent file are all locked *EXCL. ⁵ For referential constraints, the column refers to the dependent file or the dependent member. ⁶ Unique constraint or primary key constraint is a parent key in a referential constraint where the other file is a dependent file. ⁷ The other file is a parent file.