# PT-ONLINE-SCHEMA-CHANGE - possible time of running

**URL:** <https://forums.percona.com/t/pt-online-schema-change-possible-time-of-running/7123>\
**Category:** Percona Toolkit\
**Created:** [July 22, 2019, 1:07am UTC](https://forums.percona.com/t/pt-online-schema-change-possible-time-of-running/7123 "2019-07-22T01:07:46Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![le\_den](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@le\_den](https://forums.percona.com/u/le_den)\
**Post date:** [July 22, 2019, 1:07am UTC](https://forums.percona.com/t/pt-online-schema-change-possible-time-of-running/7123/1 "2019-07-22T01:07:46Z")

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Hello guys,

I would like to use PT-ONLINE-SCHEMA-CHANGE for reclaiming free space of our production DB. The things is that the DB takes 2.3TB of space, so the question is, do you maybe know how much time the PT-ONLINE-SCHEMA-CHANGE will run in order to ALTER so huge DB?

Thank you in advance,

Denis

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**Author:** ![lorraine.pocklington](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/lorraine.pocklington/32/37_2.png) [@lorraine.pocklington](https://forums.percona.com/u/lorraine.pocklington)\
**Post date:** [July 22, 2019, 6:53am UTC](https://forums.percona.com/t/pt-online-schema-change-possible-time-of-running/7123/2 "2019-07-22T06:53:11Z")

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Hi there le\_den, thanks for your question.

The dev team suggested that you could try the --dry-run option to see how long it takes to at least nibble at the table in question, from there you might be able to draw a best case estimate… Here’s a link: [https://www.percona.com/doc/percona-toolkit/LATEST/pt-online-schema-change.html#cmdoption-pt-online-schema-change-dry-run](https://www.percona.com/doc/percona-toolkit/LATEST/pt-online-schema-change.html#cmdoption-pt-online-schema-change-dry-run)

See how you get on?

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<div class="post-metadata">

**Author:** ![le\_den](https://avatars.discourse-cdn.com/v4/letter/l/e68b1a/32.png) [@le\_den](https://forums.percona.com/u/le_den)\
**Post date:** [July 22, 2019, 7:38am UTC](https://forums.percona.com/t/pt-online-schema-change-possible-time-of-running/7123/3 "2019-07-22T07:38:37Z")

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Hi Lorraine,

And thank you for prompt response. I’ll try that.