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support transaction isolation modification through reserved connection system settings #11987

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merged 1 commit into from
Jan 13, 2023
Merged

support transaction isolation modification through reserved connection system settings #11987

merged 1 commit into from
Jan 13, 2023

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harshit-gangal
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@harshit-gangal harshit-gangal commented Dec 19, 2022 •
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Description

This PR moves the transaction isolation system variables (transaction_isolation or set transaction isolation level) from vitess aware to reserved connection.
Earlier it used to only work with transactions. With this change, support will be added for read queries.

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  • "Backport to:" labels have been added if this change should be back-ported
  • Tests were added or are not required
  • Documentation was added or is not required

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@harshit-gangal
feat: support transaction isolation through reserved connection
bbf0fb1 
Signed-off-by: Harshit Gangal <harshit@planetscale.com>
@harshit-gangal harshit-gangal added Type: Enhancement Logical improvement (somewhere between a bug and feature) Component: Query Serving labels Dec 19, 2022
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vitess-bot bot commented Dec 19, 2022 •
edited by GuptaManan100
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@harshit-gangal harshit-gangal changed the title feat: support transaction isolation through reserved connection support transaction isolation modification through reserved connection system settings Dec 19, 2022
@harshit-gangal harshit-gangal marked this pull request as ready for review December 19, 2022 07:36
@harshit-gangal harshit-gangal added Type: Enhancement Logical improvement (somewhere between a bug and feature) and removed Type: Enhancement Logical improvement (somewhere between a bug and feature) labels Dec 19, 2022
GuptaManan100
GuptaManan100 reviewed Dec 19, 2022
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Everything else looks good, but isn't this like a breaking change? Previously setting the transaction isolation would only apply to the next query, but now it applies to the session, if I understand correctly. Shouldn't this be added to the release notes?

go/vt/vtgate/safe_session.go
@@ -597,10 +597,10 @@ func (session *SafeSession) SetPreQueries() []string {
first := true
for _, k := range keys {
if first {
preQuery.WriteString(fmt.Sprintf("set @@%s = %s", k, sysVars[k]))
preQuery.WriteString(fmt.Sprintf("set %s = %s", k, sysVars[k]))
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Why is this change needed?

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@harshit-gangal harshit-gangal Dec 19, 2022 •
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TLDR; previously it was broken.

@@ without any scope represents session scope. Only for the case of transaction_isolation it means the next transaction. This gets applied only once.
With the implementation of settings pool these settings will not be applied again and the connection will be reused, which means the next query the connection will see, will have the session level isolation level and not the next transaction isolation level.
So, the user expectation will turn out to be wrong.

The RFC already states that the next transaction isolation statements will be converted to the session level setting.

Now the other part of it, If the user would have set the transaction_isolation at the session level. This will get only applied for the next transaction in case of reserved connection.

deepthi
deepthi approved these changes Jan 9, 2023
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One small suggestion, rest LGTM

go/test/endtoend/vtgate/reservedconn/sysvar_test.go

// setting to different value.
utils.Exec(t, conn, "set @@transaction_isolation = 'read-committed'")
utils.AssertMatches(t, conn, "select @@transaction_isolation", `[[VARCHAR("READ-COMMITTED")]]`)
utils.AssertMatches(t, conn, "select @@transaction_isolation", `[[VARCHAR("read-committed")]]`)
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Why are some values uppercase and some lowercase?
Line 437 - REPEATABLE-READ. But everything else is lowercase.

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Looks like it may be an artifact of how the test input is provided. To avoid confusion, my suggestion is to make them all uniform.

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I will raise a separate PR to handle it.

GuptaManan100
GuptaManan100 approved these changes Jan 10, 2023
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I don't have any other comments than the ones already answered.

@harshit-gangal harshit-gangal merged commit a5a14f1 into vitessio:main Jan 13, 2023
@harshit-gangal harshit-gangal deleted the tx-isolation branch January 13, 2023 04:08
@harshit-gangal harshit-gangal mentioned this pull request Jan 16, 2023
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@harshit-gangal harshit-gangal mentioned this pull request Feb 8, 2023
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@deepthi deepthi deepthi approved these changes

@GuptaManan100 GuptaManan100 GuptaManan100 approved these changes

@systay systay Awaiting requested review from systay systay is a code owner

@frouioui frouioui Awaiting requested review from frouioui frouioui is a code owner

@arthurschreiber arthurschreiber Awaiting requested review from arthurschreiber arthurschreiber is a code owner

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set transaction isolation level extention to read queries
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@harshit-gangal @deepthi @GuptaManan100