Function AssignWriterGangFirst

src/backend/executor/execUtils.c:1880–1904

* AssignWriterGangFirst() - Try to assign writer gang first. * * For the gang allocation, our current implementation required the first * allocated gang must be the writer gang. * This has several reasons: * - For lock holding, Because of our MPP structure, we assign a LockHolder * for each segment when executing a query. lockHolder is the gang member that * should hold and manage locks

 * on reader gang. So, find the writer slice and assign writer gang first.
 */
static bool
AssignWriterGangFirst(CdbDispatcherState *ds, SliceTable *sliceTable, int sliceIndex)
{
	ExecSlice	   *slice = &sliceTable->slices[sliceIndex];

	if (slice->gangType == GANGTYPE_PRIMARY_WRITER)
	{
		Assert(slice->primaryGang == NULL);
		Assert(slice->segments != NIL);
		slice->primaryGang = AllocateGang(ds, slice->gangType, slice->segments);
		setupCdbProcessList(slice);
		return true;
	}
	else
	{
		ListCell *cell;
		foreach(cell, slice->children)
		{
			int			childIndex = lfirst_int(cell);
			if (AssignWriterGangFirst(ds, sliceTable, childIndex))
				return true;
		}
	}
	return false;
}

/*
 * Helper for AssignGangs takes a simple inventory of the gangs required