Add tidb_low_resolution_tso session scope variable on master #10428
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Low resolution timestamp is updated once every two seconds which can be used if reading slightly old version of data is acceptable. Like tidb_snapshot read, transaction is readonly when tidb_low_resolution_tso is enabled. Signed-off-by: Xiaoguang Sun <sunxiaoguang@zhihu.com>
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## master #10428 +/- ##
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zz-jason
reviewed
May 13, 2019
| type lowResolutionTsFuture uint64 | ||
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| // Wait implements the oracle.Future interface. | ||
| func (f lowResolutionTsFuture) Wait() (uint64, error) { |
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how about abbreviate Resolution to Rez or Reso? Found in https://www.abbreviations.com/abbreviation/RESOLUTION
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It does look verbose now. But i'm not sure about Rez, looks strange to me though. Let's see what other people think about it.
| @@ -140,3 +140,21 @@ func (o *pdOracle) updateTS(ctx context.Context, interval time.Duration) { | |||
| func (o *pdOracle) Close() { | |||
| close(o.quit) | |||
| } | |||
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| type lowResolutionTsFuture uint64 | |||
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please add some comment about this future.
alivxxx
reviewed
May 13, 2019
Signed-off-by: Xiaoguang Sun <sunxiaoguang@zhihu.com>
Signed-off-by: Xiaoguang Sun <sunxiaoguang@zhihu.com>
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It's strange that I have signed CLA however it kept complaining it's not done yet. |
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Finally got CLA passed after merging master |
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/run-all-tests |
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LGTM |
tiancaiamao
added
status/all tests passed
status/LGT1
zz-jason
reviewed
May 22, 2019
Signed-off-by: Xiaoguang Sun <sunxiaoguang@zhihu.com>
zz-jason
added
status/LGT2
db-storage
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to db-storage/tidb
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May 29, 2019
db-storage
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to db-storage/tidb
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May 29, 2019
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Low resolution timestamp is updated once every two seconds which can be used if reading slightly old version of data is acceptable. Like tidb_snapshot read, transaction is readonly when tidb_low_resolution_tso is enabled.
What problem does this PR solve?
Introduce a session scope variable tidb_low_resolution_tso which can use periodically updated
timestamp from TSO when transaction starts. This can save one TSO request roundtrip time per transaction which is beneficial for small readonly queries in terms of latency. As a side effect, there will be less TSO requests hence less pressure on PD.
What is changed and how it works?
Add a new tidb_low_resolution_tso session scope variable. When transaction starts and about to get start timestamp from TSO, call low resolution timestamp interface when tidb_low_resolution_tso is enabled. Like tidb_snapshot read, transaction is readonly when tidb_low_resolution_tso is enabled.
Tests
Related changes