count(distinct ...) always sorts, rather than using a hash, to do its work. I don't think that there is any fundamental reason that it could not be changed to allow it to use hashing, it just hasn't been done yet. It is complicated by the fact that you can have multiple count(...
PostgreSQL CASEs can have multiple conditions. There are a handful of entries in the table where the name of country and capital is the same. You can add this to your previously constructed CASE - SELECT name, continent, indep_year, CASE WHEN (indep_year < 1900) AND (countries.name = co...
Another option is to use range partitioning with multiple columns in the partition key. Either of these can easily lead to excessive numbers of partitions, so restraint is advisable. It is important to consider the overhead of partitioning during query planning and execution. The query planner is...
*/ StaticAssertDecl(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS, "group clog threshold less than PGPROC cached subxids"); /* * When there is contention on XactSLRULock, we try to group multiple * updates; a single leader process will perform transaction status * updates ...
If any of the upper 25/17 bits are not zero, the code point is broken into multiple 1-byte (UTF-8) or 2-byte (UTF-16) sequences based on someclever rules, One of the very nice features of Unicode is that any code point where the upper 25 bits are zero is exactly the same as...
*/ if (node->ps.ps_TupFromTlist) { Assert(projInfo); /* can't get here if not projecting */ resultSlot = ExecProject(projInfo, &isDone); if (isDone == ExprMultipleResult) return resultSlot; /* Done with that source tuple... */ node->ps.ps_TupFromTlist = false; } /* * ...
/** Identifiers for timeout reasons. Note that in case multiple timeouts * trigger at the same time, they are serviced in the order of this enum.*/typedefenumTimeoutId {/*Predefined timeout reasons*/STARTUP_PACKET_TIMEOUT, DEADLOCK_TIMEOUT, ...
That's not strictly necessary, but otherwise when you run * the same query multiple times the starting position would shift * a little bit backwards on every invocation, which is confusing. * We don't guarantee any specific ordering in general, though. */ if (scan->rs_syncscan) ss_...
When multiple workers are running, the autovacuum cost delay parameters (seeSection 20.4.4[5]) are “balanced” among all the running workers, so that the total I/O impact on the system is the same regardless of the number of workers actually running. However, any workers processing tables ...
While the declarative partitioning feature allows users to partition tables into multiple partitioned tables living on the same database server, sharding allows tables to be partitioned in a way that the partitions live on external foreign servers and the parent table lives on the primary node ...