	/* clear padding */
	memset(&key, 0, sizeof(pgssHashKey));

	key.userid = GetUserId();
	key.dbid = MyDatabaseId;
	key.queryid = queryId;
	key.toplevel = (nesting_level == 0);

	/* Lookup the hash table entry with shared lock. */
	LWLockAcquire(&pgss->lock.lock, LW_SHARED);

	entry = (pgssEntry *) hash_search(pgss_hash, &key, HASH_FIND, NULL);
…
	/* Increment the counts, except when jstate is not NULL */
	if (!jstate)
	{
		Assert(kind == PGSS_PLAN || kind == PGSS_EXEC);

		/*
		 * Grab the spinlock while updating the counters (see comment about
		 * locking rules at the head of the file)
		 */
		SpinLockAcquire(&entry->mutex);

		/* "Unstick" entry if it was previously sticky */
		if (IS_STICKY(entry->counters))
			entry->counters.usage = USAGE_INIT;

		entry->counters.calls[kind] += 1;
		entry->counters.total_time[kind] += total_time;

		if (entry->counters.calls[kind] == 1)
		{
			entry->counters.min_time[kind] = total_time;
			entry->counters.max_time[kind] = total_time;
			entry->counters.mean_time[kind] = total_time;
		}
		else
		{
			/*
			 * Welford's method for accurately computing variance. See
			 * <http://www.johndcook.com/blog/standard_deviation/>
			 */
			double		old_mean = entry->counters.mean_time[kind];

			entry->counters.mean_time[kind] +=
				(total_time - old_mean) / entry->counters.calls[kind];
			entry->counters.sum_var_time[kind] +=
				(total_time - old_mean) * (total_time - entry->counters.mean_time[kind]);

…
		entry->counters.rows += rows;
		entry->counters.shared_blks_hit += bufusage->shared_blks_hit;
		entry->counters.shared_blks_read += bufusage->shared_blks_read;
		entry->counters.shared_blks_dirtied += bufusage->shared_blks_dirtied;
		entry->counters.shared_blks_written += bufusage->shared_blks_written;

Échauffement