When requested, load the "citus" library first #3761
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| libraries := []string{"pg_stat_statements", "pgnodemx"} | ||
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| defined, found := outParameters.Mandatory.Get("shared_preload_libraries") | ||
| if found { | ||
| libraries = append(libraries, defined) | ||
| } |
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Making sure I'm following: this code here would've prepended "pg_stat_statements", "pgnodemx" to the list -- and we don't want them prepended, we want them appended, yeah?
| if strings.Contains(v, "citus") { | ||
| v = "citus," + v |
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Making sure I've got this (though the test helps):
- we want citus to be first;
- citus can be present several times without side effect;
- removing citus from that list (from the non-first position) would be brittle
Is that a fair summation?
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Is that a fair summation?
Yep.
2. citus can be present several times without side effect;
There is a set of related parameters for loading libraries that amount to LOAD statements at certain times.
- https://www.postgresql.org/docs/current/runtime-config-client.html#RUNTIME-CONFIG-CLIENT-PRELOAD
- https://www.postgresql.org/docs/current/sql-load.html
If the file has been loaded already, the command does nothing.
Postgres compares inodes to detect symlink chains as well.
3. removing citus from that list (from the non-first position) would be brittle
A variety of names can refer to the same library. As I recall, citus, citus.so, and a full path are acceptable. This does not handle the full path case, but in my experience that is quite unusual.
Being more deliberate with these names requires parsing, which #3530 did partially. Ultimately, matching on names is still a step removed from the issue: the Citus code that complains could be in a file with any name. 
Issue: PGO-284 Issue: CrunchyData#3194
Checklist:
Type of Changes:
What is the current behavior (link to any open issues here)?
User-defined libraries are loaded last. #3194
What is the new behavior (if this is a feature change)?
When included in user-defined libraries,
citusis loaded first.Other Information:
Fixes: #3194
Replaces: #3530
Resolves:#2915