Show memory usage

[Krysztophe]

Is your feature request related to a problem? Please describe.

I don't see a way to detect a huge memory use.

• Example: https://explain.dalibo.com/plan/4ah1g688ae6b7fbd#plan/node/1
  The Sort uses 3 Go in memory. This is visible in Misc but not obvious.

So a user would be happy to eradicate temp files, but would not be conscious that he now uses gigabytes of RAM.

• Other example with 2 sorts and 2x1.5GB sorts: https://explain.dalibo.com/plan/b1dea32h3de72bd5#plan

Describe the solution you'd like

• On nodes, change IO & Buffers to: IO & Memory
  Add a Memory line for each type, first of all Sort Memory.

• This place seems logical because there are already the temp tables here.
  For example, in https://explain.dalibo.com/plan/ggc4a71be9hfaecd#plan/node/2, temp tables are in local buffers…
  Perhaps add a line converting these local tables as Temp Memory.

• Add another line for the memory of the Planning phase: eg. https://explain.dalibo.com/plan/dee6c1ad8cg1g2bd#plan/node/2 (not a problem usually but good to know)

• There must be some place to show the cumulated memory use in the whole plan (this is a worst case, the memory used by first nodes may be released before the last nodes begin).

• I have probably forgotten other places where memory is used.

• It's known that, in many places, the used memory is not reported by EXPLAIN (like the shared memory for the parallel workers communication).

• Anyway: known memory consumption above some threshold (hard to say how much… 500 MB ?) should trigger another small red or orange icon on the node.

Describe alternatives you've considered

• Another Memory entry among time/rows/buffers/IO ?