Bug #116031 mysqlsh instanceDump --includeSchemas="" behavior

Description:
Using the instanceDump utility to dump users only is easily accomplished with the --includeSchemas parameter. One can specify a non-existent schema, or a space: --includeSchemas=" ", but an empty string: --includeSchemas="", dumps all databases.

$ mysqlsh --version
mysqlsh   Ver 8.0.29 for Linux on x86_64 - for MySQL 8.0.29 (MySQL Community Server (GPL))

I ran a dedeployer loop on a couple versions of Percona Server with an empty string for includeSchemas (no space):

DBDBASE=/opt/percona_server/;
SANDBOX=test_instDump
while read h; do 
echo -e "version is: $h\n";
  dbdeployer deploy single ${DBDBASE}$h --port=22238 --sandbox-directory=${SANDBOX}.$h --skip-library-check --force
  mkdir /home/dov.endress/sandboxes/backup/$h
  mysql --port=22238 --socket=/tmp/mysql_sandbox22238.sock -umsandbox -pmsandbox -e 'CREATE DATABASE test_instanceDump';
  mysqlsh  --socket=/tmp/mysql_sandbox22238.sock --user=msandbox -pmsandbox --host=localhost -- util dumpInstance /home/dov.endress/sandboxes/backup/$h --threads=1 --users=true --consistent=false --includeSchemas="" 2>&1 | tee -a /home/dov.endress/sandboxes/backup/$h.instDump.log
  ls -larth /home/dov.endress/sandboxes/${SANDBOX}.$h/data/ >> /home/dov.endress/sandboxes/backup/$h/$h.instDump.log
  ls -larth /home/dov.endress/sandboxes/backup/$h/ >> /home/dov.endress/sandboxes/backup/$h/$h.instDump.log
  dbdeployer delete ${SANDBOX}.$h
 done < ps.versions

Both instances dumped all schemata available to mysqlsh dumpInstance:

version is: 5.7.35

Database installed in $HOME/sandboxes/test_instDump.5.7.35
run 'dbdeployer usage single' for basic instructions'
.. sandbox server started
...
Total duration: 00:00:00s
Schemas dumped: 2
Tables dumped: 0
...
version is: 8.0.36

Database installed in $HOME/sandboxes/test_instDump.8.0.36
run 'dbdeployer usage single' for basic instructions'
... sandbox server started
2 out of 6 schemas will be dumped and within them 0 tables, 0 views.
13 out of 16 users will be dumped.  

And the subsequent files generated:

$ ls ~/sandboxes/backup/5.7.35
5.7.35.instDump.log  @.done.json  @.json  @.post.sql  @.sql  test_instanceDump.json  test_instanceDump.sql  test.json  test.sql  @.users.sql
$ ls ~/sandboxes/backup/8.0.36
8.0.36.instDump.log  @.done.json  @.json  @.post.sql  @.sql  test_instanceDump.json  test_instanceDump.sql  test.json  test.sql  @.users.sql

The same test but with includeSchemas=" " (with space) behaves as expected:

version is: 5.7.35

Database installed in $HOME/sandboxes/test_instDump.5.7.35
run 'dbdeployer usage single' for basic instructions'
.. sandbox server started
...
Total duration: 00:00:00s
Schemas dumped: 0
Tables dumped: 0
...
version is: 8.0.36

Database installed in $HOME/sandboxes/test_instDump.8.0.36
run 'dbdeployer usage single' for basic instructions'
... sandbox server started
...
Gathering information...
0 out of 6 schemas will be dumped and within them 0 tables, 0 views.
13 out of 16 users will be dumped.  

The same test was performed using MySQL Community 5.7.36 and 8.0.32 with the same results as expected.

How to repeat:
Start an instance 5.7 or greater and create a new database (instanceDump will not dump information_schema, mysql, ndbinfo, performance_schema, or sys by design).

Execute instanceDump with includeSchemas=""

 mysqlsh  --user=* -p* --host=* -- util dumpInstance --threads=1 --users=true --consistent=false --includeSchemas=""

Newly created schema will be noted as dumped and dump file created.

Suggested fix:
I leave it up to you as to whether this should be a feature request: make "" behave the same as " " or alternatively add userDropOnly option to mimic functionality and error on includeSchemas=" " (or non-existent schema), an actual 'bug' that should be fixed, or a documentation update to make the behavior clearly known.

Given that other tools, i.e. mysql cli and mysqldump will error on a non-existent schema, I would lean toward adding the option to dump user info only and have mysqlsh error on includeSchemas=" " or includeSchemas="<schema_that_does_not_exist>" for consistency sake alone.

While a minor and somewhat edge case, this behavior could be devastating to the user who unwisely writes a backup to the same volume as their data directory.

Cheers!
Dov Endress

Hello Dov Endress,

Thank you for the report and feedback.

Thanks,
Umesh