Add capability to create consistent transactions by systay · Pull Request #4310 · vitessio/vitess

systay · 2018-10-24T14:34:57Z

To make this possible, two things are added:

The capability to lock all tables on a tablet, to momenterily stop updates
Once the database is locked, we can create multiple consistent snapshot
transactions that all share the same view of the data

This PR is part of a larger piece of work to allow consistent snapshot to be used when cloning and diffing, instead of pausing replication.

sougou

Approach looks good overall. Got some initial comments/questions.
I still need to think about the consequences of stream connection using tx pool.

There is an intent to merge the stream and non-stream protocol. So, we need to make decisions that are compatible with that future. Most likely, it's not material for this change.

sougou · 2018-10-27T22:55:45Z

go/mysql/flavor_mariadb.go

Looks like there is an equivalent for mariadb: https://mariadb.com/kb/en/library/start-slave/

go/vt/vttablet/tabletserver/tx_pool.go

go/vt/vttablet/tabletserver/tabletserver.go

go/vt/vttablet/tabletserver/query_executor.go

sougou

Will it be possible to write integration tests for this feature? For example, how do we know this will work as expected for MariaDB?

Let me know if you need help/guidance for this.

go/vt/vttablet/tabletserver/tabletenv/config.go

tirsen · 2018-11-12T16:37:52Z

test/lock_tables.py

maybe extract this to a method on Tablet? so you can do just:

tablet_manager = tablet_replica1.connect_tablet_manager() tablet_manager.LockTables(...)

tirsen · 2018-11-12T16:39:40Z

test/lock_tables.py

should we also have a test for auto-unlock on timeout? Maybe if you expose that as a flag then set it to something really low like 1 second when you start the tablet and then you sleep for 2 seconds and the tables should be unlocked?

sougou

This is looking good so far. I assume you're still working on the integration tests?

sougou · 2018-11-16T22:50:40Z

go/vt/vttablet/tabletserver/tabletserver.go

 }

 func (tsv *TabletServer) serveNewType() (err error) {
+	if !tsv.te.isOpen {


nit: this is not necessary. The state machine ensures that serveNewType will not get called without a fullStart. This is also the reason why this code doesn't need to ensure that other services like qe are already open.

I actually put this in here to make cache_invalidation.py green again. Not sure what is going on there, but if I comment these three lines out, that test starts failing.

It just occurred to me that cache_invalidation did expose a problem with the approach of opening te in fullStart. Essentially, we have to close and re-open te every time serveNewType gets called. This is because Close will have to wait for existing transactions to be resolved before we can switch to the new serving type.

In other words, we should go back to the old behavior, except that we immediately te.Open as soon as it's closed.

systay · 2018-11-17T09:21:26Z

@sougou correct. Still working on adding more integration tests.

systay · 2018-11-22T10:10:51Z

@sougou @deepthi I think the necessary tests are there now. I think we should squash before merging to clean the history - just wanted to keep the commits separate so you can easily track the changes.

systay · 2018-11-29T08:34:16Z

@sougou @deepthi status for this PR is that I still have not solved #4310 (comment)

other than that, I think it's ready

sougou · 2018-12-15T22:14:55Z

go/vt/vttablet/tabletserver/tabletserver_test.go

Why did you delete these tests (this and the ReplicaToMaster)? Are they failing? If so, we need to investigate why.

These are important because they prove that no errors will be served during state transitions.

They were removed by mistake. Sorry about that, and thanks for catching it!

The tests are related to the 5a449d1 commit. I don't think that change is correct, and the tests agree :)

sougou · 2018-12-18T23:15:13Z

The tests need to be looked at. They're failing after a restart also.

sougou · 2019-01-08T18:42:57Z

go/vt/vttablet/tabletserver/tabletserver.go

Moving this to TxEngine introduces a race:

Thread 1: tsv.Begin is called, which calls startRequest through execRequest.

Thread 1: tsv.mu is released once startRequest returns.

Thread 2: A call to setServingType is received.

Thread 2: goes in: there are no begin requests in the wait group. So, it closes the TxEngine, or changes its state.

Thread 1: TxEngine.Begin executes on a TxEngine, which adds to the beginWaitGroup. But the state is not the same as what it was when startRequest returned, potentially causing unexpected behavior.

sougou · 2019-01-08T18:45:10Z

go/vt/vttablet/tabletserver/tabletserver.go

I don't think we need this interface. We should introduce interfaces only if it's necessary, like if there is a need to replace teCtrl with something else. Otherwise, directly using TxEngine is generally more readable.

FWIW I disagree. In my opinion interfaces more clearly delineates how different parts of the code interact and make it more obvious when you add a new dependency across a code base. It is one of the most powerful tools we humans have to tackle complexity by breaking down code in smaller parts so that we can understand each part separately without having to understand everything at the same time.

Sugu, you might be able to keep all of Vitess in your head at the same time. Us mortals are not as fortunate. We have to page different parts in and out.

:-)

In this particular case, I won't insist if you think the interface helps.

The reason why I dislike interfaces is because of the opposite reason: I can't hold the codebase in my head :).
Here's a classic example: https://github.com/vitessio/vitess/blob/master/go/vt/vtgate/scatter_conn.go#L146. This particular line calls into queryservice. As a challenge, you can try drilling down to figure what code path gets eventually used to call vttablet.
Another similar situation is with TabletStats that report health. I still don't understand how that mechanism works, and this has prevented me from fixing issues in that area. I know the health check mechanism is broken; People keep reporting strange issues. But there's nothing I can do there. Those interface abstractions make it impossible for me to understand what calls what.

Short story long: in this case, it's fairly obvious one way or another.

To make this possible, two things are added: - The capability to lock all tables on a tablet, to momenterily stop updates - Once the database is locked, we can create multiple consistent snapshot transactions that all share the same view of the data - Adds the capability to have replication move forward to a specific point in the transaction log Signed-off-by: Andres Taylor <antaylor@squareup.com>

Signed-off-by: Andres Taylor <antaylor@squareup.com>

go/vt/vttablet/tabletmanager/rpc_lock_tables.go

Signed-off-by: Andres Taylor <antaylor@squareup.com>

* upstream/master: Skip ACL checks for dual pseudotable Makes sure the schema engine has started up before getting debug information. Support tables that have columns named desc exec_cases: add passing messages OnDup test exec_cases: add failing tests for msgs on dupe planbuilder: support ‘on duplicate key’ for msgs

This reverts commit a57c799. Signed-off-by: Andres Taylor <antaylor@squareup.com>

* upstream/master: helm: release 1.0.5 vreplication: address review comments tlstest_test: Go 1.12 / TLS 1.3 fix vreplication: vstream final tweaks vreplication: tests are done vreplication: handle singleton and mariadb issues vreplication: moved tests into vstreamer dir vreplication: more vstreamer tests vreplication: MariaDB test tweaks and more tests vreplication: tests: statements and DDL add column vreplication: make a singleton srvtopo.Server vreplication: got some basic tests working vreplication: tabletserver inits and other tweaks vreplication: vstreamer, plan and filtering vreplication: streamer planbuilder vreplication: vstreamer Engine Signed-off-by: Andres Taylor <antaylor@squareup.com>

Signed-off-by: Andres Taylor <antaylor@squareup.com>

* upstream/master: vtctl: run BackupShard on replica, rdonly or spare Expose `glog.MaxSize` as `-log_rotate_max_size` flag inline ok check; while-range instead of bare while test the signal handler reload db-credentials-file upon SIGHUP change ClusterAlias in _vt.local_metadata to be keyspace/shard instead of keyspace.shard Signed-off-by: Andres Taylor <antaylor@squareup.com>

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>

Signed-off-by: Andres Taylor <antaylor@squareup.com>

* upstream/master: Adds a test to check regressions in parser Adding in SQL commands to prepare an instance to join an existing shard Revert "Support tables that have columns named desc" Use a truly random Destination for DestinationAnyShard Signed-off-by: Andres Taylor <antaylor@squareup.com>

sougou · 2019-01-17T18:10:10Z

go/vt/vttablet/tabletserver/tabletserver_test.go

 		t.Errorf("Prepared queries: %v, want %v", got, want)
 	}
-	tsv.SetServingType(topodatapb.TabletType_REPLICA, true, nil)
+	tsv.SetServingType(topodatapb.TabletType_MASTER, false, nil)


Shouldn't this be REPLICA?

sougou · 2019-01-17T18:10:49Z

go/vt/vttablet/tabletserver/tabletserver_test.go

-	tsv.SetServingType(topodatapb.TabletType_REPLICA, true, nil)
+	tsv.SetServingType(topodatapb.TabletType_MASTER, false, nil)
+	if len(tsv.te.preparedPool.conns) != 0 {
+		t.Fatal("fail")


Change this to t.Errorf with a more clear error message (and down below).

sougou · 2019-01-17T18:15:42Z

Strangely, a previous comment disappeared. The test you commented out as obsolete, you can delete that. The test failures look real. One of them is failing to compile, and another one has a data race.

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Trying to make it clearer what we are testing. Signed-off-by: Andres Taylor <antaylor@squareup.com>

systay · 2019-01-18T15:28:37Z

Maybe use #4533 instead?

systay changed the title ~~Add capability create consistent transactions~~ Add capability to create consistent transactions Oct 24, 2018

sougou reviewed Oct 28, 2018

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systay force-pushed the lock-tables branch 3 times, most recently from c862c97 to 34a916e Compare November 1, 2018 15:34

sougou reviewed Nov 4, 2018

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go/vt/vttablet/tabletserver/tabletenv/config.go Outdated Show resolved Hide resolved

systay force-pushed the lock-tables branch 3 times, most recently from d0f9fba to 9dcb4b7 Compare November 12, 2018 16:31

tirsen approved these changes Nov 12, 2018

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systay force-pushed the lock-tables branch from 223c4e0 to 6653672 Compare November 16, 2018 12:08

sougou reviewed Nov 16, 2018

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systay force-pushed the lock-tables branch 3 times, most recently from 1680352 to 0f179a0 Compare November 22, 2018 09:27

systay mentioned this pull request Nov 27, 2018

Shard splitting using consistent snapshots #4395

Closed

systay force-pushed the lock-tables branch from 6a45999 to 2cca4b7 Compare November 29, 2018 08:32

systay force-pushed the lock-tables branch 2 times, most recently from 82ae29e to 5a449d1 Compare December 5, 2018 10:46

sougou reviewed Dec 15, 2018

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systay force-pushed the lock-tables branch from d150132 to 2cd7829 Compare December 17, 2018 13:53

systay force-pushed the lock-tables branch from ebec14f to d1d4f90 Compare December 27, 2018 12:33

systay force-pushed the lock-tables branch from d9de565 to 383f533 Compare January 8, 2019 09:53

sougou reviewed Jan 8, 2019

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Andres Taylor added 2 commits January 10, 2019 14:08

Always restart the engine when changing server type

d7cb371

Signed-off-by: Andres Taylor <antaylor@squareup.com>

mpawliszyn reviewed Jan 10, 2019

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go/vt/vttablet/tabletmanager/rpc_lock_tables.go Outdated Show resolved Hide resolved

Andres Taylor added 5 commits January 11, 2019 09:42

Don't touch the internals unnecessarily

5785cdd

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Prepare tests for read only transactions

1ee033c

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Moving code around to make it easier to read

e0e52e5

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Reject write transactions when in read only mode

fabc520

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Make sure the schema engine is initialized

f99a185

Signed-off-by: Andres Taylor <antaylor@squareup.com>

systay force-pushed the lock-tables branch from 3334bdf to f99a185 Compare January 11, 2019 13:02

Andres Taylor added 5 commits January 11, 2019 15:18

Check for null

caaad26

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Revert "Split test file in two to get around test harness problem"

611ec92

This reverts commit a57c799. Signed-off-by: Andres Taylor <antaylor@squareup.com>

Comments

830917d

Signed-off-by: Andres Taylor <antaylor@squareup.com>

systay force-pushed the lock-tables branch from 9098326 to 830917d Compare January 14, 2019 18:18

Andres Taylor and others added 7 commits January 15, 2019 11:45

Return tx_engine to the old behaviours of rolling back transactions

05826a1

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Minor refactoring

3966d01

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Continue restoring the old behaviour back

20ba0f5

Signed-off-by: Andres Taylor <antaylor@squareup.com>

temp fix for tx pool hang

4fafca8

Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>

Make sure to not start 2PC when in read-only mode

79f7894

Signed-off-by: Andres Taylor <antaylor@squareup.com>

sougou reviewed Jan 17, 2019

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Andres Taylor added 4 commits January 18, 2019 09:47

Clean up test code

d9882d8

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Fix compilation error

3c5b742

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Fix data race

16a95a3

Signed-off-by: Andres Taylor <antaylor@squareup.com>

Test code clean up

21303bb

Trying to make it clearer what we are testing. Signed-off-by: Andres Taylor <antaylor@squareup.com>

systay mentioned this pull request Jan 18, 2019

Add capability create consistent transactions #4533

Merged

systay closed this Jan 18, 2019

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