Tom Lane wrote:
I looked at this but did not actually see the code path that requires forcing creation of the per-DB entry right at this spot. The HASH_FIND calls for this hashtable seem to all happen on the backend side not the collector side. Can you explain why we need this?
Yeah, I missed this when making the original change (this code is rather opaque :-\). The problem is that if we don't initialize the dbentry for the database we connect to, it won't get written out to the statsfile in pgstat_write_statsfile(). So the database won't be counted as having any backends connected to it in pgstat_read_statsfile() (see line 2558 of pgstat.c in HEAD).
BTW, the comment at line 2210 of pgstat.c is misleading: the n_backends in the entries of the dbentry hash table are explicitly ignored when reading in the stats file -- the value is instead derived from the number of beentries that are seen.
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