Fix checking cancelled connections back into the connection pool #1095
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
KJTsanaktsidis
force-pushed
the
ktsanaktsidis/PEN-734/fix_isolation_level_cancel
branch
from
649efc7
to
dee6989
Compare
kunwardeep
approved these changes
May 11, 2020
|
Github didn't get the memo but if you click through to the travis build it's green. |
kunwardeep
previously approved these changes
May 12, 2020
methane
reviewed
May 12, 2020
driver_test.go
Outdated
| if err != nil { | ||
| dbt.Fatal(err) | ||
| } | ||
|
|
||
| // Delay execution for just a bit until db.ExecContext has begun. | ||
| defer time.AfterFunc(100*time.Millisecond, cancel).Stop() | ||
| go time.AfterFunc(100*time.Millisecond, cancel) |
There was a problem hiding this comment.
I actually didn't understand how this was working at all - what it looked like it should be doing was canceling the context whilst the SQL was executing SLEEP(1), so I turned it into this.
I just read the docs for time.AfterFunc more carefully and I think we can just invoke it on the main goroutine instead of calling go?
There was a problem hiding this comment.
Eurgh - ok the problem is I just don't know how defer works. This is going to cause time.AfterFunc() to run now, and then Stop() to run when the method returns. I'll change it back.
KJTsanaktsidis
force-pushed
the
ktsanaktsidis/PEN-734/fix_isolation_level_cancel
branch
from
dee6989
to
1b73282
Compare
methane
reviewed
May 12, 2020
If
* BeginTx is called with a non-default isolation level,
* The context is canceled before SET TRANSACTION ISOLATION LEVEL
completes,
then the connection:
* has the cancelled property set to "context cancelled",
* has the closed property set to true,
and,
* BeginTx returns "context canceled"
Because of this, the connection gets put back into the connection pool.
When it is checked out again, if BeginTx is called on it again _without_
an isolation level,
* then we fall into the mc.closed.IsSet() check in begin(),
* so we return ErrBadConn,
* so the driver kicks the broken connection out of the pool
* (and transparently retries to get a new connection that isn't
broken too).
However, if BeginTx is called on the connection _with_ an isolation
level, then we return a context canceled error from the SET TRANSACTION
ISOLATION LEVEL call.
That means the broken connection will stick around in the pool forever
(or until it's checked out for some other operation that correctly
returns ErrBadConn).
The fix is to check for the connection being closed before executing SET
TRANSACTION ISOLATION LEVEL.
KJTsanaktsidis
force-pushed
the
ktsanaktsidis/PEN-734/fix_isolation_level_cancel
branch
from
1b73282
to
978b6bd
Compare
methane
approved these changes
May 12, 2020
|
Thank you for a quick review & merge! |
tz70s
pushed a commit
to tz70s/mysql
that referenced
this pull request
Sep 5, 2020
…sql-driver#1095) If * BeginTx is called with a non-default isolation level, * The context is canceled before SET TRANSACTION ISOLATION LEVEL completes, then the connection: * has the cancelled property set to "context cancelled", * has the closed property set to true, and, * BeginTx returns "context canceled" Because of this, the connection gets put back into the connection pool. When it is checked out again, if BeginTx is called on it again _without_ an isolation level, * then we fall into the mc.closed.IsSet() check in begin(), * so we return ErrBadConn, * so the driver kicks the broken connection out of the pool * (and transparently retries to get a new connection that isn't broken too). However, if BeginTx is called on the connection _with_ an isolation level, then we return a context canceled error from the SET TRANSACTION ISOLATION LEVEL call. That means the broken connection will stick around in the pool forever (or until it's checked out for some other operation that correctly returns ErrBadConn). The fix is to check for the connection being closed before executing SET TRANSACTION ISOLATION LEVEL.
tz70s
pushed a commit
to tz70s/mysql
that referenced
this pull request
Sep 5, 2020
…sql-driver#1095) If * BeginTx is called with a non-default isolation level, * The context is canceled before SET TRANSACTION ISOLATION LEVEL completes, then the connection: * has the cancelled property set to "context cancelled", * has the closed property set to true, and, * BeginTx returns "context canceled" Because of this, the connection gets put back into the connection pool. When it is checked out again, if BeginTx is called on it again _without_ an isolation level, * then we fall into the mc.closed.IsSet() check in begin(), * so we return ErrBadConn, * so the driver kicks the broken connection out of the pool * (and transparently retries to get a new connection that isn't broken too). However, if BeginTx is called on the connection _with_ an isolation level, then we return a context canceled error from the SET TRANSACTION ISOLATION LEVEL call. That means the broken connection will stick around in the pool forever (or until it's checked out for some other operation that correctly returns ErrBadConn). The fix is to check for the connection being closed before executing SET TRANSACTION ISOLATION LEVEL.
jsha
added a commit
to jsha/mysql
that referenced
this pull request
May 20, 2021
…ool (go-sql-driver#1095)" This reverts commit 6313f20.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Description
If
then the connection:
and,
Because of this, the connection gets put back into the connection pool. When it is checked out again, if BeginTx is called on it again without an isolation level,
However, if BeginTx is called on the connection with an isolation
level, then we return a context canceled error from the SET TRANSACTION
ISOLATION LEVEL call.
That means the broken connection will stick around in the pool forever
(or until it's checked out for some other operation that correctly
returns ErrBadConn).
The fix is to check for the connection being closed before executing SET
TRANSACTION ISOLATION LEVEL.
Checklist