Explain Part 3 – Visual Explain

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5 Responses

  1. sandip says:

    Aren’t access plans read left-to-right, top-to-bottom? Your article says right-to-left. Can you please verify?

    • Ember Crooks says:

      Well, the most important thing is bottom to top. The first thing DB2 does is the lowest thing. Then if there is more than one action on that level, we must go right to left if we want to understand the order DB2 is doing things in. The true way to tell what DB2 is doing in what order is always to look at the operator identifiers. In the example in this post, DB2 is doing the ixscan/fetch on SCHSTATUS on the right first, before it does the ixscan/fetch on SCHCONFIG. It may not hurt to read it left to right, as nothing that is dependent on something else will be on on the same level. But to read it in the order that db2 is taking actions, right to left is the way to go.

  2. sandip says:

    Sorry I meant bottom to top which is what you have written too. Question is about left to right.

  3. Steve Ling says:

    How can I clean up explain tables?

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