> > My initial thought is that this patch does not remove the issue of > > loading the entire query text (just to return one or a few entries). > > This patch is not intended to address the issue of loading the file > with query texts. We only try to avoid forming and handling tuples > that we don't really need. Forming a tuple in > pg_stat_statements_internal() includes calling CStringGetTextDatum(), > which allocates memory and copies the query text. Avoiding that for > queries we don't need makes a big difference already.
Yes, but my point is, if someone repeatedly lookup up pg_stat_statements with filters, they will end up loading the query text multiple times. for example: ```` select * from pg_stat_statements where query_id in (10000, 20000, 30000); ``` will only load the query text once to retrieve these 3 query IDs. If I instead do this, with the proposed patch: ``` select * from pg_stat_statements(true, queryid=>10000); select * from pg_stat_statements(true, queryid=>20000); select * from pg_stat_statements(true, queryid=>30000); or select * from pg_stat_activity a, pg_stat_statements(true, queryid=>a.query_id); ``` I will have to load the query text file into memory for every invocation of pg_stat_statements. > > For what it is worth, I have been thinking about what it would take to > > move query texts into shared memory, which could make this type of > > filtering more practical. > > As far as I can tell, pg_stat_statements is storing query texts in an > external file to not have problems with long query texts. Here is a > quote from the docs: > > > The representative query texts are kept in an external disk file, and > > do not consume shared memory. Therefore, even very lengthy query texts > > can be stored successfully. pg_stat_statements_internal must load the file when showtext = true, which is the default. ``` qbuffer = qtext_load_file(&qbuffer_size); ``` -- Sami Imseih Amazon Web Services (AWS)
