【JVM】生产内存占用异常优化（一）

记录一次 - 内存占用优化

某个导出，导出数据量过大总是导致OOM，但是根据需求，导出数据大小并没有那么大

按照导出数据的查询来看

 SELECTg.inventory_code,g.visit_record_code,g.recovery_price AS transactionAmount
FROM
crm_goods g
...
...

三个字段大小预计大小100W数据应该是不大于100m的，但是现实是1个G都不够用，果断开启MAT,查看最大对象如下
在这里插入图片描述
震惊，100w个单纯对象声明，竟然占用了1.3GB内存，于是我测试了一下原对象全部字段和单纯查询三个字段声明100W个的差距

		ArrayList<VisitGoodsInfoResp> visitGoodsInfoResps = new ArrayList<>(1000000);ArrayList<VisitGoodsInfoExport> visitGoodsInfoExports = new ArrayList<>(1000000);for (int i = 0; i < 1000000; i++) {VisitGoodsInfoResp visitGoodsInfoResp1 = new VisitGoodsInfoResp();visitGoodsInfoResps.add(visitGoodsInfoResp1);VisitGoodsInfoExport visitGoodsInfoExport1 = new VisitGoodsInfoExport();visitGoodsInfoExports.add(visitGoodsInfoExport1);}

MAT分析如下
在这里插入图片描述

两个竟然差距如此之大，我们使用jol工具看下两个对象的差距

com.VisitGoodsInfoResp object internals:OFFSET  SIZE                      TYPE DESCRIPTION                                          VALUE0     4                           (object header)                                      01 00 00 00 (00000001 00000000 00000000 00000000) (1)4     4                           (object header)                                      00 00 00 00 (00000000 00000000 00000000 00000000) (0)8     4                           (object header)                                      05 c2 00 f8 (00000101 11000010 00000000 11111000) (-134168059)12     4          java.lang.String VisitGoodsInfoResp.inventoryCode                     null16     4          java.lang.String VisitGoodsInfoResp.name                              null...... 省略N个字段...652     4          java.lang.String VisitGoodsInfoResp.dockingCustomerDeptName           null656     4   java.time.LocalDateTime VisitGoodsInfoResp.registrationTime                  null660     4      java.math.BigDecimal VisitGoodsInfoResp.salesTransitCount                 null
Instance size: 664 bytes
Space losses: 0 bytes internal + 0 bytes external = 0 bytes totalcom.VisitGoodsInfoExport object internals:OFFSET  SIZE                   TYPE DESCRIPTION                               VALUE0     4                        (object header)                           01 00 00 00 (00000001 00000000 00000000 00000000) (1)4     4                        (object header)                           00 00 00 00 (00000000 00000000 00000000 00000000) (0)8     4                        (object header)                           8b c3 00 f8 (10001011 11000011 00000000 11111000) (-134167669)12     4       java.lang.String VisitGoodsInfoExport.inventoryCode        null16     4   java.math.BigDecimal VisitGoodsInfoExport.transactionAmount    null20     4       java.lang.String VisitGoodsInfoExport.visitRecordCode      null
Instance size: 24 bytes
Space losses: 0 bytes internal + 0 bytes external = 0 bytes total