RE: [Patch] Optimize dropping of relation buffers using dlist

Hello Kirk,

I noticed you have pushed a new version for your patch which has some changes on TRUNCATE on TOAST relation. 
Although you've done performance test for your changed part. I'd like to do a double check for your patch(hope you
don'tmind).
 
Below is the updated recovery performance test results for your new patch. All seems good.

*TOAST relation with PLAIN strategy like integer : 
1. Recovery after VACUUM test results(average of 15 times)
shared_buffers        master(sec)        patched(sec)     %reg=((patched-master)/patched)
--------------------------------------------------------------------------------------
128M            2.111             1.604             -24%
10G            57.135             1.878             -97%
20G            167.122         1.932             -99%

2. Recovery after TRUNCATE test results(average of 15 times)
shared_buffers      master(sec)       patched(sec)     %reg=((patched-master)/patched)
--------------------------------------------------------------------------------------
128M            2.326             1.718             -26%
10G            82.397             1.738             -98%
20G            169.275         1.718             -99%

*TOAST relation with NON-PLAIN strategy like text/varchar: 
1. Recovery after VACUUM test results(average of 15 times)
shared_buffers        master(sec)        patched(sec)     %reg=((patched-master)/patched)
--------------------------------------------------------------------------------------
128M            3.174             2.493             -21%
10G            72.716             2.246             -97%
20G            163.660         2.474             -98%

2. Recovery after TRUNCATE test results(average of 15 times): Although it looks like there are some improvements after
patchapplied. I think that's because of the average calculation. TRUNCATE results should be similar between master and
patchedbecause they all do full scan.
 
shared_buffers      master(sec)       patched(sec)     %reg=((patched-master)/patched)
--------------------------------------------------------------------------------------
128M            4.978             4.958             0%
10G            97.048             88.751             -9%
20G            183.230         173.226         -5% 

[Machine spec]
CPU : 40 processors  (Intel(R) Xeon(R) Silver 4210 CPU @ 2.20GHz)
Memory: 128G
OS: CentOS 8

[Failover test data]
Total table Size: 600M
Table: 10000 tables (1000 rows per table)

[Configure in postgresql.conf]
autovacuum = off
wal_level = replica
max_wal_senders = 5
max_locks_per_transaction = 10000

If you have any questions on my test results, please let me know.

Regards
Tang