Speed up regular result iterator

[mattmundell]

What:

Speed up iterator created by init_result_get_iterator:

1. Simplify level check when checking for all levels.
2. Use LATERAL to keep the new severity SQL in a single place in the statement.
3. Inline SQL from views and functions to take advantage of the JOIN on table nvts.
4. Use WITH to isolate the current severity calculation in the "overrides on, dynamic on" case.

Improvements to my GET_RESULTS times:

static, overrides off      17s to 6s
static, overrides on      248s to 34s
dynamic, overrides off     45s to 6s
dynamic, overrides on     415s to 33s

This translates to similar jumps in the GSA Results page.

This PR is similar to the changes to the result counting iterator in #1358.

Why:

Improves the speed of the GSA result pages when using bigger dbs, especially the Results page.

Making the dynamic cases fast may enable us to switch to "query-time" dynamic-only severity (#1337).

How did you test it:

With an 800k result db, having 3 overrides.

1. git checkout master

2. make install

3. gvmd

4. update settings set value = 0 where owner = (select id from users where name = 'm') and uuid = '77ec2444-e7f2-4a80-a59b-f4237782d93f';

5. time o m m '<get_results details="1" filter="apply_overrides=0 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/master-st => 17s

6. time o m m '<get_results details="1" filter="apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/master-st-ov => 248s

7. update settings set value = 1 where owner = (select id from users where name = 'm') and uuid = '77ec2444-e7f2-4a80-a59b-f4237782d93f';

8. time o m m '<get_results details="1" filter="apply_overrides=0 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/master-dy => 45s

9. time o m m '<get_results details="1" filter="apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/master-dy-ov => 415s

10. time o m m '<get_results details="1" filter="rexec apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/master-dy-ov-filter => 209s (with pg jit off)

11. git checkout lateral-results

12. make install

13. gvmd

14. update settings set value = 1 where owner = (select id from users where name = 'm') and uuid = '77ec2444-e7f2-4a80-a59b-f4237782d93f';

15. time o m m '<get_results details="1" filter="apply_overrides=0 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/lateral-st => 6s

16. time o m m '<get_results details="1" filter="apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/lateral-st-ov => 34s

17. update settings set value = 1 where owner = (select id from users where name = 'm') and uuid = '77ec2444-e7f2-4a80-a59b-f4237782d93f';

18. time o m m '<get_results details="1" filter="apply_overrides=0 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/lateral-dy => 5s

19. time o m m '<get_results details="1" filter="apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/lateral-dy-ov => 33s

20. time o m m '<get_results details="1" filter="rexec apply_overrides=1 min_qod=70 sort-reverse=severity rows=10 first=1"/>' > /tmp/lateral-dy-ov-filter => 73s (with pg jit off)

21. cd /tmp

22. diff master-st lateral-st => empty

23. diff master-st-ov lateral-st-ov => empty

24. diff master-dy lateral-dy => empty

25. diff master-dy-ov lateral-dy-ov => empty

26. diff master-dy-ov-filter lateral-dy-ov-filter => empty

Checklist:

• Tests
• CHANGELOG Entry