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't mind).
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 patch applied. I think that's because of the average calculation. TRUNCATE results should be similar between master and patched because 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