how dose count(1) works？

[kevin]

hi,all
    I have a test about hbase run top of alluxio . In my hbase there is a
table a create by phoenix an have 2880404 rows. I can run : count "A"  on
hbase ,but not on phoenix(select count(1) from A),if I do so,hbase region
server will crash.
so I want to know how dose count(1) works？what is the different between the
tow way when I do the same thing?