Online DDL: ddl_strategy=direct

[shlomi-noach]

Backport

NO

Status

ready

Description

Following an internal discussion, where @askdba noticed this output:

 vtctlclient ApplySchema -sql="$(cat create_commerce_schema.sql)" commerce
Handling connection for 15999
I1213 17:07:05.817487   35734 main.go:64] I1213 14:07:05.661886 tablet_executor.go:259] Received DDL request. strategy =
I1213 17:07:05.882329   35734 main.go:64] I1213 14:07:05.729416 tablet_executor.go:259] Received DDL request. strategy =

strategy = (empty) seems confusing. Up till now, the empty string stood for the "direct" (non-online) DDL strategy.

Starting this PR, the dircet (non-online) strategy is named "direct". Consider the following examples:

mysql> select @@ddl_strategy;
+----------------+
| @@ddl_strategy |
+----------------+
| direct         |
+----------------+
1 row in set (0.00 sec)

mysql> alter table corder modify order_id int;
Query OK, 0 rows affected (0.03 sec)

mysql> set @@ddl_strategy='gh-ost';
Query OK, 0 rows affected (0.00 sec)

mysql> alter table corder modify order_id int;
+--------------------------------------+
| uuid                                 |
+--------------------------------------+
| 1305a8e4_3dd5_11eb_85ea_f875a4d24e90 |
+--------------------------------------+
1 row in set (0.00 sec)

mysql> set @@ddl_strategy='';
Query OK, 0 rows affected (0.00 sec)

mysql> alter table corder modify order_id int;
Query OK, 0 rows affected (0.01 sec)

/tmp/local$ vtctlclient ApplySchema -sql "alter table corder modify order_id int" commerce
I1214 08:25:23.239231 1630821 main.go:64] I1214 06:25:23.238050 tablet_executor.go:272] Received DDL request. strategy=direct
/tmp/local$ vtctlclient ApplySchema -ddl_strategy "gh-ost" -sql "alter table corder modify order_id int" commerce
I1214 08:25:38.917898 1630847 main.go:64] I1214 06:25:38.917187 tablet_executor.go:272] Received DDL request. strategy=gh-ost
I1214 08:25:38.918173 1630847 main.go:64] I1214 06:25:38.917839 tablet_executor.go:308] UUID=2ee751f1_3dd5_11eb_a6e5_f875a4d24e90
2ee751f1_3dd5_11eb_a6e5_f875a4d24e90
/tmp/local$ vtctlclient ApplySchema -ddl_strategy "" -sql "alter table corder modify order_id int" commerce
I1214 08:25:44.846210 1630860 main.go:64] I1214 06:25:44.844765 tablet_executor.go:272] Received DDL request. strategy=direct

notes:

• in vtgate, the default value for -ddl_strategy command line flag is direct. An empty value is also interpreted as direct.
• likewise, in vtctl/vtctlclient, the default value for -ddl_strategy command line flag is direct. An empty value is also interpreted as direct.

Related Issue(s)

Tracking: #6926

Todos

• Tests
• Documentation

Impacted Areas in Vitess

List general components of the application that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build

[shlomi-noach]

Documentation in vitessio/website#639

[askdba]

Did we intentionally used dd_strategy instead of ddl_strategy?

likewise, in vtctl/vtctlclient, the default value for -dd_strategy command line flag is direct. An empty value is also interpreted as direct.```

[shlomi-noach]

Did we intentionally used dd_strategy instead of ddl_strategy?

That's just a typo in my comment. Fixed.

[askdba]

On the MySQL CLI I've got the same results as above test case.

Query OK, 0 rows affected (0.00 sec)

MySQL [commerce]> alter table corder modify order_id int;
+--------------------------------------+
| uuid                                 |
+--------------------------------------+
| fc1d1705_404a_11eb_b95d_0242ac110002 |
+--------------------------------------+
1 row in set (0.00 sec)

MySQL [commerce]>
MySQL [commerce]>
MySQL [commerce]> set @@ddl_strategy='direct';
Query OK, 0 rows affected (0.00 sec)

MySQL [commerce]> alter table corder modify order_id int;
Query OK, 0 rows affected (0.01 sec)

But on the command line, I did not get the same output.

vitess@5c644a6f4170:/vt/local$ vtctlclient ApplySchema -sql "alter table corder modify order_id bigint" commerce
vitess@5c644a6f4170:/vt/local$ vtctl --version
ERROR: logging before flag.Parse: E1217 09:36:03.895258    1618 syslogger.go:149] can't connect to syslog
Version: d65877152 (Git branch 'ddl-strategy-direct') built on Thu Dec 17 09:15:19 UTC 2020 by vitess@ecd12ae46f97 using go1.13.15 linux/amd64

[shlomi-noach]

But on the command line, I did not get the same output.

That's because since this PR was opened, I already merged another PR that removes that log line altogether. If you'd like the log line to appear please let me know.

[askdba]

I've found the log message useful. I'd like it back.

[shlomi-noach]

Log message is now restored.

[shlomi-noach]

🙏 request for additional review

[ajm188]

lgtm

[indera-shsp]

nit pick: explciitly

[indera-shsp]

Perhaps it is useful to log the sql too 🤷‍♂️