修复mysql协议连接场景的内存泄漏问题 · Pull Request !2087 · openGauss/Plugin

1. Free mem in dolphin proto.
---

【标题】(请简要描述下实现的内容)
修复mysql协议连接场景的内存泄漏问题
【实现内容】:
修复mysql协议连接场景的内存泄漏问题

【根因分析】:
通过DBE_PERF.track_memory_context可观测到内存持续增长的位置为 read_com_stmt_exec_request 函数中的parameter_types相关内存，将相关内容插入hash表前，没有判断是否条目已存在，导致重复赋值内存，内存未释放

【实现方案】:
如果hash表中条目已存在，先释放原来的内存，再赋值。同时优化了几个小点的内存使用和释放

【关联需求或issue】:
【测试类型：SQL功能】【测试版本：7.0.0-RC2】TPCC-MYSQL 加载数据阶段内存持续增长
https://gitee.com/opengauss/Plugin/issues/IC2L7L

【开发自验报告】:
1. 请附上自验结果(内容或者截图)
tpcc_load过程中，持续观测gs_session_memory_detail 视图，无明显异常，SessionCacheMemoryContext内存没有持续增长
```
proto_test_db=# select contextname, sum(totalsize)/1024/1024 sum, sum(freesize)/1024/1024, count(*) count from gs_session_memory_detail group by contextname order by sum desc limit 10;
           contextname           |          sum           |        ?column?        | count
---------------------------------+------------------------+------------------------+-------
 LocalSysCacheShareMemoryContext |    65.9467926025390625 |    15.6713867187500000 |    29
 LocalSysCacheTopMemoryContext   |    30.3638000488281250 |    12.3649139404296875 |    29
 ThreadTopMemoryContext          | 8.62639617919921875000 | 0.20315551757812500000 |    29
 DefaultTopMemoryContext         | 8.57773590087890625000 | 0.52371978759765625000 |    29
 gs_signal                       | 8.04536437988281250000 | 2.18811035156250000000 |     1
 Undo Recycler                   | 8.00788879394531250000 | 0.00767517089843750000 |     1
 CBBTopMemoryContext             | 6.85838317871093750000 | 0.75202178955078125000 |    29
 LocalSysCacheMyDBMemoryContext  | 2.64062500000000000000 | 1.02285766601562500000 |    29
 Timezones                       | 2.30943298339843750000 | 0.07655334472656250000 |    29
 PLpgSQL function cache          | 1.98000335693359375000 | 0.00263977050781250000 |     1
(10 rows)

proto_test_db=# select contextname, sum(totalsize)/1024/1024 sum, sum(freesize)/1024/1024, count(*) count from gs_session_memory_detail group by contextname order by sum desc limit 10;
           contextname           |          sum           |        ?column?        | count
---------------------------------+------------------------+------------------------+-------
 LocalSysCacheShareMemoryContext |    65.9467926025390625 |    15.6713867187500000 |    29
 LocalSysCacheTopMemoryContext   |    30.3638000488281250 |    12.3649139404296875 |    29
 ThreadTopMemoryContext          | 8.62639617919921875000 | 0.20159912109375000000 |    29
 DefaultTopMemoryContext         | 8.57773590087890625000 | 0.52371978759765625000 |    29
 gs_signal                       | 8.04536437988281250000 | 2.18811035156250000000 |     1
 Undo Recycler                   | 8.00788879394531250000 | 0.00767517089843750000 |     1
 CBBTopMemoryContext             | 6.85838317871093750000 | 0.75202178955078125000 |    29
 LocalSysCacheMyDBMemoryContext  | 2.64062500000000000000 | 1.02285766601562500000 |    29
 Timezones                       | 2.30943298339843750000 | 0.07655334472656250000 |    29
 PLpgSQL function cache          | 1.98000335693359375000 | 0.00263977050781250000 |     1
(10 rows)

proto_test_db=# select contextname, sum(totalsize)/1024/1024 sum, sum(freesize)/1024/1024, count(*) count from gs_session_memory_detail group by contextname order by sum desc limit 10;
           contextname           |          sum           |        ?column?        | count
---------------------------------+------------------------+------------------------+-------
 LocalSysCacheShareMemoryContext |    65.9467926025390625 |    15.6713867187500000 |    29
 LocalSysCacheTopMemoryContext   |    30.3638000488281250 |    12.3649139404296875 |    29
 ThreadTopMemoryContext          | 8.62639617919921875000 | 0.20315551757812500000 |    29
 DefaultTopMemoryContext         | 8.57773590087890625000 | 0.52371978759765625000 |    29
 gs_signal                       | 8.04536437988281250000 | 2.18811035156250000000 |     1
 Undo Recycler                   | 8.00788879394531250000 | 0.00767517089843750000 |     1
 CBBTopMemoryContext             | 6.85838317871093750000 | 0.75202178955078125000 |    29
 LocalSysCacheMyDBMemoryContext  | 2.64062500000000000000 | 1.02285766601562500000 |    29
 Timezones                       | 2.30943298339843750000 | 0.07655334472656250000 |    29
 PLpgSQL function cache          | 1.98000335693359375000 | 0.00263977050781250000 |     1

```
2. 是否可以添加fastcheck测试用例，如是，请补充fastcheck用例
否。fastcheck暂时难以覆盖
3. 是否涉及资料修改，如是，在docs仓库补充资料
不涉及
4. 是否考虑支撑升级和在线扩容等扩展场景。涉及升级/回滚脚本修改的场景请按如下方式测试验证升级/回滚是否正常，并提供自验截图。注意 `2.0`， `3.0` 为dolphin插件版本，请根据实际情况选择。
```
alter system set upgrade_mode to 2;
select pg_sleep(2);
begin;
set isinplaceupgrade to on;
set dolphin.b_compatibility_mode = off;
alter extension dolphin update to '2.0';
alter extension dolphin update to '3.0';
reset dolphin.b_compatibility_mode;
abort;

alter system set upgrade_mode to 0;
```
不涉及
5. 是否考虑异常场景/并发场景/前向兼容/性能场景
不涉及
6. 是否对其他模块产生影响
不涉及
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