etcdserver: prune revisions before send backend readTx when rangekeys

[xrmzju]

fix issue 12301

[xrmzju]

this improves performance tremendously for request WithLastRev() or WithFristRev() option when key range is big
without this pr:

[root@edd2693ca788 /]# time ./etcdctl  get --prefix=true /default/ --last-rev=true --keys-only -wjson --command-timeout=60s
{"header":{"cluster_id":11136150232382961551,"member_id":4898650950304686290,"revision":1337662,"raft_term":23},"kvs":[{"key":"L2RlZmF1bHQvQjFDVFl5d0ZxSVFpb2ZHMXBPcXpiVGtBbWVKTFQyZGc=","create_revision":1337662,"mod_revision":1337662,"version":1}],"more":true,"count":1317250}

real	0m35.135s
user	0m0.031s
sys	0m0.022s

with this pr

[root@edd2693ca788 /]# time ./etcdctl   get --prefix=true /default/ --last-rev=true --keys-only -wjson
{"header":{"cluster_id":11136150232382961551,"member_id":4898650950304686290,"revision":1337662,"raft_term":22},"kvs":[{"key":"L2RlZmF1bHQvQjFDVFl5d0ZxSVFpb2ZHMXBPcXpiVGtBbWVKTFQyZGc=","create_revision":1337662,"mod_revision":1337662,"version":1}],"more":true,"count":1317250}

real	0m0.892s
user	0m0.027s
sys	0m0.023s

[xrmzju]

@xiang90 @gyuho @jpbetz @jingyih @spzala please take a look. thx.

[xrmzju]

i don't see why the ci build failed ,can somebody help me...

[tangcong]

=== RUN TestV3RangeRequest
TestV3RangeRequest: v3_grpc_test.go:1514: #4.3: key[0]. got = a, want = c,
--- FAIL: TestV3RangeRequest (1.12s)

@xrmzju can you take a look at this failed test case?

[xrmzju]

=== RUN TestV3RangeRequest
TestV3RangeRequest: v3_grpc_test.go:1514: #4.3: key[0]. got = a, want = c,
--- FAIL: TestV3RangeRequest (1.12s)

@xrmzju can you take a look at this failed test case?

fixed

[xrmzju]

if u guys have any other feedbacks, please let me know, many thanks! @gyuho @jpbetz @jingyih @tangcong @cfc4n

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.