support Etcd as meta engine

[davies]

This PR support Etcd as meta engine.

the meta-url should be

etcd://host1:port,host2:port,host3:port/prefix?cert=/path/to/cert 

Parameters for TLS:

cacert=/path/to/file
cert=/path/to/file
key=/path/to/file
server-name=xxx
insecure-skip-verify=1

[davies]

The performance of etcd without --unsafe-no-fsync

Summary:
  Total:	2.7779 secs.
  Slowest:	0.1099 secs.
  Fastest:	0.0003 secs.
  Average:	0.0278 secs.
  Stddev:	0.0277 secs.
  Requests/sec:	35.9980

Response time histogram:
  0.0003 [1]	|
  0.0112 [14]	|∎∎∎∎∎∎∎∎
  0.0222 [66]	|∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
  0.0332 [2]	|∎
  0.0441 [2]	|∎
  0.0551 [0]	|
  0.0660 [0]	|
  0.0770 [2]	|∎
  0.0880 [3]	|∎
  0.0989 [8]	|∎∎∎∎
  0.1099 [2]	|∎

Latency distribution:
  10% in 0.0010 secs.
  25% in 0.0185 secs.
  50% in 0.0195 secs.
  75% in 0.0206 secs.
  90% in 0.0919 secs.
  95% in 0.0946 secs.
  99% in 0.1099 secs.

[solracsf]

What about ?

sudo ionice -c2 -n0 -p `pgrep etcd`

[codecov-commenter]

Codecov Report

Merging #1638 (2755e16) into main (f55ba44) will increase coverage by 0.05%.
The diff coverage is 78.04%.

@@            Coverage Diff             @@
##             main    #1638      +/-   ##
==========================================
+ Coverage   61.70%   61.76%   +0.05%     
==========================================
  Files         134      135       +1     
  Lines       22721    22924     +203     
==========================================
+ Hits        14020    14159     +139     
- Misses       7126     7169      +43     
- Partials     1575     1596      +21     

Impacted Files	Coverage Δ
pkg/meta/tkv_etcd.go	77.77% <77.77%> (ø)
pkg/meta/tkv_prefix.go	96.61% <80.00%> (+0.18%)	⬆️
pkg/meta/tkv.go	76.55% <100.00%> (+0.02%)	⬆️
pkg/vfs/reader.go	81.56% <0.00%> (-3.11%)	⬇️
pkg/chunk/cached_store.go	77.32% <0.00%> (-1.19%)	⬇️
pkg/meta/sql.go	67.13% <0.00%> (ø)
pkg/meta/sql_lock.go	74.67% <0.00%> (+2.59%)	⬆️

---

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[davies]

What about ?

sudo ionice -c2 -n0 -p `pgrep etcd`

no ionice in macOS . I have test etcd with default options in Linux, it works well.

[SandyXSD]

Benchmarks of TiKV vs ETCD (both have 3 nodes with an SSD backend):

TiKV

goos: linux
goarch: amd64
pkg: github.com/juicedata/juicefs/pkg/meta
cpu: Intel(R) Xeon(R) Platinum 8124M CPU @ 3.00GHz
BenchmarkTKV/mkdir-4         	     624	   1930961 ns/op
BenchmarkTKV/mvdir-4         	     537	   2265382 ns/op
BenchmarkTKV/rmdir-4         	     470	   2453943 ns/op
BenchmarkTKV/readdir_10-4    	     913	   1467893 ns/op
BenchmarkTKV/readdir_1k-4    	     148	   7942530 ns/op
BenchmarkTKV/mknod-4         	     633	   1980034 ns/op
BenchmarkTKV/create-4        	     604	   1941095 ns/op
BenchmarkTKV/rename-4        	     546	   2248436 ns/op
BenchmarkTKV/unlink-4        	     517	   2316809 ns/op
BenchmarkTKV/lookup-4        	    1384	    855186 ns/op
BenchmarkTKV/getattr-4       	    2636	    423620 ns/op
BenchmarkTKV/setattr-4       	     856	   1600443 ns/op
BenchmarkTKV/access-4        	    2758	    426041 ns/op
BenchmarkTKV/setxattr-4      	     916	   1259769 ns/op
BenchmarkTKV/getxattr-4      	    3541	    410169 ns/op
BenchmarkTKV/removexattr-4   	     710	   1694803 ns/op
BenchmarkTKV/listxattr_1-4   	    3356	    416820 ns/op
BenchmarkTKV/listxattr_10-4  	    2686	    432606 ns/op
BenchmarkTKV/link-4          	     746	   1561034 ns/op
BenchmarkTKV/symlink-4       	     751	   1816562 ns/op
BenchmarkTKV/newchunk-4      	  813643	      1599 ns/op
BenchmarkTKV/write-4         	     592	   2032517 ns/op
BenchmarkTKV/read_1-4        	13819200	        83.72 ns/op
BenchmarkTKV/read_10-4       	15336248	        77.55 ns/op
PASS
ok  	github.com/juicedata/juicefs/pkg/meta	49.437s

ETCD

goos: linux
goarch: amd64
pkg: github.com/juicedata/juicefs/pkg/meta
cpu: Intel(R) Xeon(R) Platinum 8124M CPU @ 3.00GHz
BenchmarkTKV/mkdir-4         	     594	   2247327 ns/op
BenchmarkTKV/mvdir-4         	     424	   2797362 ns/op
BenchmarkTKV/rmdir-4         	     415	   2873579 ns/op
BenchmarkTKV/readdir_10-4    	     754	   1670520 ns/op
BenchmarkTKV/readdir_1k-4    	      64	  18056631 ns/op
BenchmarkTKV/mknod-4         	     535	   2261128 ns/op
BenchmarkTKV/create-4        	     538	   2336013 ns/op
BenchmarkTKV/rename-4        	     376	   3206458 ns/op
BenchmarkTKV/unlink-4        	     441	   2939707 ns/op
BenchmarkTKV/lookup-4        	     860	   1385068 ns/op
BenchmarkTKV/getattr-4       	    1641	    697641 ns/op
BenchmarkTKV/setattr-4       	     722	   1586305 ns/op
BenchmarkTKV/access-4        	    1864	    624945 ns/op
BenchmarkTKV/setxattr-4      	    1459	    823831 ns/op
BenchmarkTKV/getxattr-4      	    1777	    708389 ns/op
BenchmarkTKV/removexattr-4   	     751	   1487221 ns/op
BenchmarkTKV/listxattr_1-4   	    4288	    283127 ns/op
BenchmarkTKV/listxattr_10-4  	    3648	    324412 ns/op
BenchmarkTKV/link-4          	     548	   2358875 ns/op
BenchmarkTKV/symlink-4       	     505	   2434128 ns/op
BenchmarkTKV/newchunk-4      	  714043	      1617 ns/op
BenchmarkTKV/write-4         	     454	   2483883 ns/op
BenchmarkTKV/read_1-4        	14152519	        81.26 ns/op
BenchmarkTKV/read_10-4       	14680340	        75.63 ns/op
PASS
ok  	github.com/juicedata/juicefs/pkg/meta	45.249s