Re: shared-memory based stats collector - v70 - Mailing list pgsql-hackers
From | Drouvot, Bertrand |
---|---|
Subject | Re: shared-memory based stats collector - v70 |
Date | |
Msg-id | 394d309c-ece2-75b4-9959-9f4537001359@amazon.com Whole thread Raw |
In response to | Re: shared-memory based stats collector - v70 (Andres Freund <andres@anarazel.de>) |
List | pgsql-hackers |
Hi, On 8/18/22 1:30 AM, Andres Freund wrote: > Hi, > > On 2022-08-17 15:46:42 -0400, Greg Stark wrote: >> Isn't there also a local hash table used to find the entries to reduce >> traffic on the shared hash table? Even if you don't take a snapshot >> does it get entered there? There are definitely still parts of this >> I'm working on a pretty vague understanding of :/ > Yes, there is. But it's more about code that generates stats, rather than > reporting functions. While there's backend local pending stats we need to have > a refcount on the shared stats item so that the stats item can't be dropped > and then revived when those local stats are flushed. What do you think about something along those lines for the reporting part only? Datum pgstat_fetch_all_tables_stats(PG_FUNCTION_ARGS) { int dbid = PG_ARGISNULL(0) ? -1 : (int) PG_GETARG_OID(0); ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo; dshash_seq_status hstat; PgStatShared_HashEntry *p; PgStatShared_Common *stats_data; /* Only members of pg_read_all_stats can use this function */ if (!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS)) { aclcheck_error(ACLCHECK_NO_PRIV, OBJECT_FUNCTION, "pgstat_fetch_all_tables_stats"); } pgstat_assert_is_up(); SetSingleFuncCall(fcinfo, 0); dshash_seq_init(&hstat, pgStatLocal.shared_hash, false); while ((p = dshash_seq_next(&hstat)) != NULL) { Datum values[PG_STAT_GET_ALL_TABLES_STATS_COLS]; bool nulls[PG_STAT_GET_ALL_TABLES_STATS_COLS]; PgStat_StatTabEntry * tabentry = NULL; MemSet(values, 0, sizeof(values)); MemSet(nulls, false, sizeof(nulls)); /* If looking for specific dbid, ignore all the others */ if (dbid != -1 && p->key.dboid != (Oid) dbid) continue; /* If the entry is not of kind relation then ignore it */ if (p->key.kind != PGSTAT_KIND_RELATION) continue; /* If the entry has been dropped then ignore it */ if (p->dropped) continue; stats_data = dsa_get_address(pgStatLocal.dsa, p->body); LWLockAcquire(&stats_data->lock, LW_SHARED); tabentry = pgstat_get_entry_data(p->key.kind, stats_data); values[0] = ObjectIdGetDatum(p->key.dboid); values[1] = ObjectIdGetDatum(p->key.objoid); values[2]= DatumGetInt64(tabentry->tuples_inserted); values[3]= DatumGetInt64(tabentry->tuples_updated); values[4]= DatumGetInt64(tabentry->tuples_deleted); . . . tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls); LWLockRelease(&stats_data->lock); } dshash_seq_term(&hstat); return (Datum) 0; } I also tried to make use of pgstat_get_entry_ref() but went into a failed assertion: pgstat_get_entry_ref -> dshash_find -> ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table) due to lock acquired by dshash_seq_next(). Regards, -- Bertrand Drouvot Amazon Web Services: https://aws.amazon.com
pgsql-hackers by date: