High heap overhead in com.mysql.jdbc.NonRegisteringDriver

Issue

• We are seeing high heap overhead with many com.mysql.jdbc.JDBC4Connections held by com.mysql.jdbc.NonRegisteringDriver's PhantomReferences.

Class Name                                                                                       | Ref. Objects | Shallow Heap | Ref. Shallow Heap | Retained Heap
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[0] class com.mysql.jdbc.NonRegisteringDriver @ 0x665777c30                                      |       39,102 |          112 |         1,251,264 | 2,206,971,072
'- connectionPhantomRefs java.util.concurrent.ConcurrentHashMap @ 0x665818b08                    |       39,102 |           64 |         1,251,264 | 2,206,968,312
   '- table java.util.concurrent.ConcurrentHashMap$Node[65536] @ 0x6f862cf70                     |       39,102 |      262,160 |         1,251,264 | 2,206,968,248
      |- [57508] java.util.concurrent.ConcurrentHashMap$Node @ 0x6b40678e0                       |            6 |           32 |               192 |       339,520
      |  |  |- val, key com.mysql.jdbc.NonRegisteringDriver$ConnectionPhantomReference @ 0x6836da350|            1 |           32 |                32 |        56,552