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Q: How to use EXPLAIN tables?
Answer:
PLAN_TABLE primary output. DSN_STATEMNT_TABLE for cost. DSN_FUNCTION_TABLE for functions. INSERT EXPLAIN before statement. Query tables after. PLANNO, ACCESSTYPE, MATCHCOLS important columns.
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Q: How to pass data between steps?
Answer:
Use DISP=PASS to pass datasets. Receiving step references same DSN. Or use symbolic parameters. GDG allows relative references (+1 created, 0 passed). Temporary datasets (&& prefix) auto-pass. SYSIN instream data copied to subsequent steps.
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Q: How to define GDG in JCL?
Answer:
Create GDG base with IDCAMS DEFINE GDG. Reference generations: DSN=MY.GDG(+1) for new, DSN=MY.GDG(0) for current, DSN=MY.GDG(-1) for previous. DISP=(NEW,CATLG) for +1. Model DSCB needed for SMS-managed datasets.
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Q: What is symbolic parameter?
Answer:
Symbols are variables: SET symbol=value or &symbol on JOB/PROC. Reference: DSN=&HLQ..DATA. Resolved at job entry. EXEC proc,symbol=value overrides. SET statement defines. Symbols start with & and up to 8 characters.
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Q: How to concatenate datasets?
Answer:
Stack DD statements: //INPUT DD DSN=FILE1,DISP=SHR // DD DSN=FILE2,DISP=SHR. No DD name on continuation. Read consecutively as one file. Different LRECL needs LRECL on first DD or DCB parameter. Concatenation limit varies by system.
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Q: How to define VSAM in JCL?
Answer:
//DD DD DSN=VSAM.CLUSTER,DISP=SHR for existing. New cluster needs IDCAMS DEFINE CLUSTER. JCL references cluster, not data/index. AMP parameter for VSAM options: AMP=(BUFNI=8,BUFND=4). Cannot create VSAM with JCL alone.
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Q: Explain NULLFILE keyword?
Answer:
NULLFILE is alternate for DUMMY. //DD DD NULLFILE. Discards output, provides EOF for input. DSN=NULLFILE equivalent. No actual dataset. Useful for testing without actual files.
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Q: Explain DD PATH statement?
Answer:
PATH specifies Unix/USS file. PATH='/u/user/file'. Used instead of DSN. PATHDISP for disposition. PATHOPTS for options. PATHMODE for permissions. Integrates USS files into batch JCL.
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Q: What causes INVALID DATA SET NAME?
Answer:
Dataset name violates rules: 44 char max, qualifier 8 max, start with letter/national, periods separate qualifiers, no double periods, no special characters. Check spelling, length, valid characters.
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Q: How to reference PDS member?
Answer:
DSN=PDS.NAME(MEMBER). Direct member reference. DISP must allow access. For input, member must exist. For output, overwrites or creates. IEBCOPY for multiple members. Member name 1-8 characters.
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Q: What is profile table?
Answer:
Profile tables store user-specific optimizer settings. DSN_PROFILE_TABLE, DSN_PROFILE_ATTRIBUTES. Override defaults for specific statements. Use QUERYNO correlation. Advanced tuning technique.
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Q: What is zparm?
Answer:
ZPARM (DSNZPARMs) are DB2 installation parameters. Control system behavior, limits, defaults. DSNZPARM module loaded at startup. Changes need restart usually. Critical for performance and security tuning.
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Q: What causes VSAM file status 35?
Answer:
Status 35 is file not found. Check: DSN spelling, catalog entry exists, IDCAMS LISTCAT confirms. JCL DD name matches program. May need to define cluster first. Common for new programs.
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Q: Explain DD DUMMY statement
Answer:
DD DUMMY discards output/provides EOF for input. No I/O actually performed. DUMMY, DSN=NULLFILE equivalent. Use to skip optional outputs or provide empty input. Program sees immediate EOF on read. Writes succeed but discarded.
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Q: Explain referback DD
Answer:
Referback references earlier DD: DSN=*.STEP1.DDNAME or DSN=*.DDNAME (same step). Copies DSN and DISP. Can override other parameters. VOL=REF=*.STEP1.DD copies volume. Useful for chained processing.
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Q: How to define temporary dataset?
Answer:
Temporary datasets: DSN=&&TEMP or omit DSN. Exist for job duration only. Not cataloged. Passed between steps with DISP=PASS. Automatically deleted at job end. Example: //WORK DD DSN=&&TEMP,UNIT=SYSDA,SPACE=(CYL,5)
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Q: What is IEFBR14?
Answer:
IEFBR14 is null program (Branch to Register 14 = return). Returns immediately. Used for dataset management: create, delete, catalog datasets. //DELETE EXEC PGM=IEFBR14 //DD DD DSN=name,DISP=(MOD,DELETE). Common for housekeeping.
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Q: How to define PDS?
Answer:
//PDSOUT DD DSN=MY.PDS,DISP=(NEW,CATLG),SPACE=(CYL,(5,1,10)),DCB=(RECFM=FB,LRECL=80). Directory blocks (10) required for PDS. Or DSNTYPE=LIBRARY for PDSE. PDSE allows dynamic directory expansion, member-level sharing.
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Q: How does IEFBR14 delete work?
Answer:
//DEL EXEC PGM=IEFBR14 //DD DD DSN=file,DISP=(MOD,DELETE). If file exists, DISP=(MOD,DELETE) deletes. If not exists, MOD creates then deletes (empty). Or DISP=(OLD,DELETE) fails if not exists. Common pattern for cleanup.
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Q: What causes NOTCAT error?
Answer:
NOTCAT means dataset not in catalog. Check: correct DSN spelling, dataset was cataloged, catalog searched is correct. Use DISP=SHR only for cataloged datasets. DISP=OLD with VOL=SER for uncataloged. LISTCAT verifies catalog entry.
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Q: How to allocate PDSE?
Answer:
DSNTYPE=LIBRARY creates PDSE. Better than PDS: dynamic directory, member-level sharing, no compression needed. Or DATACLAS with PDSE attribute. Cannot convert back to PDS easily. Recommended for new PDSes.
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Q: How to override PROC DD?
Answer:
//procstep.ddname DD overrides. //MYSTEP.SYSOUT DD SYSOUT=H changes SYSOUT class. Can add parameters or replace entirely. Add new DD: //MYSTEP.NEWDD DD DSN=... Position after EXEC procname.