Multiple pg_waldump --rmgr options

I wanted to dump all heap WAL records with pg_waldump, so I did this:

> $ pg_waldump --rmgr=heap --rmgr=heap2 data/pg_wal/000000010000000000000001 --stat=record
> Type N (%) Record size (%) FPI size (%) Combined size (%)
> ---- - --- ----------- --- -------- --- ------------- ---
> Heap2/PRUNE 268 ( 8.74) 18192 ( 2.73) 0 ( 0.00) 18192 ( 1.74)
> Heap2/VACUUM 55 ( 1.79) 4940 ( 0.74) 0 ( 0.00) 4940 ( 0.47)
> Heap2/FREEZE_PAGE 277 ( 9.03) 186868 ( 28.03) 0 ( 0.00) 186868 ( 17.86)
> Heap2/VISIBLE 467 ( 15.23) 27783 ( 4.17) 376832 ( 99.34) 404615 ( 38.68)
> Heap2/MULTI_INSERT 1944 ( 63.38) 354800 ( 53.21) 2520 ( 0.66) 357320 ( 34.16)
> Heap2/MULTI_INSERT+INIT 56 ( 1.83) 74152 ( 11.12) 0 ( 0.00) 74152 ( 7.09)
> -------- -------- -------- --------
> Total 3067 666735 [63.74%] 379352 [36.26%] 1046087 [100%]
> pg_waldump: fatal: error in WAL record at 0/1680118: invalid record length at 0/1680150: wanted 24, got 0

That didn't do what I wanted. It only printed the Heap2 records, not
Heap, even though I specified both. The reason is that if you specify
multiple --rmgr options, only the last one takes effect.

I propose the attached to allow selecting multiple rmgrs, by giving
multiple --rmgr options. With that, it works the way I expected:

> $ pg_waldump --rmgr=heap --rmgr=heap2 data/pg_wal/000000010000000000000001 --stat=record
> Type N (%) Record size (%) FPI size (%) Combined size (%)
> ---- - --- ----------- --- -------- --- ------------- ---
> Heap2/PRUNE 268 ( 1.77) 18192 ( 0.71) 0 ( 0.00) 18192 ( 0.55)
> Heap2/VACUUM 55 ( 0.36) 4940 ( 0.19) 0 ( 0.00) 4940 ( 0.15)
> Heap2/FREEZE_PAGE 277 ( 1.83) 186868 ( 7.33) 0 ( 0.00) 186868 ( 5.67)
> Heap2/VISIBLE 467 ( 3.09) 27783 ( 1.09) 376832 ( 50.37) 404615 ( 12.27)
> Heap2/MULTI_INSERT 1944 ( 12.86) 354800 ( 13.91) 2520 ( 0.34) 357320 ( 10.83)
> Heap2/MULTI_INSERT+INIT 56 ( 0.37) 74152 ( 2.91) 0 ( 0.00) 74152 ( 2.25)
> Heap/INSERT 9948 ( 65.80) 1433891 ( 56.22) 8612 ( 1.15) 1442503 ( 43.73)
> Heap/DELETE 942 ( 6.23) 50868 ( 1.99) 0 ( 0.00) 50868 ( 1.54)
> Heap/UPDATE 193 ( 1.28) 101265 ( 3.97) 9556 ( 1.28) 110821 ( 3.36)
> Heap/HOT_UPDATE 349 ( 2.31) 36910 ( 1.45) 1300 ( 0.17) 38210 ( 1.16)
> Heap/LOCK 209 ( 1.38) 11481 ( 0.45) 316828 ( 42.35) 328309 ( 9.95)
> Heap/INPLACE 212 ( 1.40) 44279 ( 1.74) 32444 ( 4.34) 76723 ( 2.33)
> Heap/INSERT+INIT 184 ( 1.22) 188803 ( 7.40) 0 ( 0.00) 188803 ( 5.72)
> Heap/UPDATE+INIT 15 ( 0.10) 16273 ( 0.64) 0 ( 0.00) 16273 ( 0.49)
> -------- -------- -------- --------
> Total 15119 2550505 [77.32%] 748092 [22.68%] 3298597 [100%]
> pg_waldump: fatal: error in WAL record at 0/1680150: invalid record length at 0/16801C8: wanted 24, got 0

- Heikki