一段简单的代码访问postgres的文件利用空余时间写了一段代码，该程序每次读取postgres数据文件的一个数据块，将该数据块的数据解析出来。然后对该数据块中的每一条记录进行解析。从后面的测试可以看出，当对一条记录进行了update操作之后，该条记录在数据块中会有两条记录。他们的t_infomask2值分别是#defineHEAP_MOVED_OFF0x4000/*movedtoanotherplace*/#defineHEAP_MOVED_IN0x8000/*movedfromanotherplace*/如果一条记录被更新两次，中间一次的infomask2会是0xc000,即移入然后移出。测试使用的数据表中有两个字段:idint,txtvarvhar(15).在打印出的紧跟TupleHeader之后的数据可以看出:前4个字节是保存的id,后面的字节保存着txt。因为txt是变长数据，所以第五个字节是长度(0x21:0x01代表长度用1字节保存，(0x20>>1)代表实际的长度16)。从第六个字节开始是txt数据的ASCII码。1.代码[root@PGsteven]#catreader.h#ifndefX_READER_H#defineX_READER_H#include<stdio.h>#include<stdlib.h>#include<fcntl.h>#include<string.h>#defineBLCKSZ(1024*8)#defineZBUFFER_SIZE(BLCKSZ+1)#defineFLEXIBLE_ARRAY_MEMBER1typedefunsignedcharuint8;/*==8bits*/typedefunsignedshortuint16;/*==16bits*/typedefunsignedintuint32;/*==32bits*/typedefsignedcharint8;/*==8bits*/typedefsignedshortint16;/*==16bits*/typedefsignedintint32;/*==32bits*/typedefuint32TransactionId;typedefuint32CommandId;typedefuint32LocalTransactionId;typedefuint32SubTransactionId;typedefuint16LocationIndex;typedefunsignedintOid;typedefuint16OffsetNumber;typedefuint8bits8;/*>=8bits*/typedefuint16bits16;/*>=16bits*/typedefuint32bits32;/*>=32bits*/typedefstruct{uint32xlogid;/*highbits*/uint32xrecoff;/*lowbits*/}PageXLogRecPtr;typedefstructItemIdData{unsignedlp_off:15,/*offsettotuple(fromstartofpage)*/lp_flags:2,/*stateofitempointer,seebelow*/lp_len:15;/*bytelengthoftuple*/}ItemIdData;typedefstructBlockIdData{uint16bi_hi;uint16bi_lo;}BlockIdData;typedefstructItemPointerData{BlockIdDataip_blkid;OffsetNumberip_posid;}ItemPointerData;typedefstructPageHeaderData{/*XXXLSNismemberof*any*block,notonlypage-organizedones*/PageXLogRecPtrpd_lsn;/*LSN:nextbyteafterlastbyteofxlog*recordforlastchangetothispage*/uint16pd_checksum;/*checksum*/uint16pd_flags;/*flagbits,seebelow*/LocationIndexpd_lower;/*offsettostartoffreespace*/LocationIndexpd_upper;/*offsettoendoffreespace*/LocationIndexpd_special;/*offsettostartofspecialspace*/uint16pd_pagesize_version;TransactionIdpd_prune_xid;/*oldestprunableXID,orzeroifnone*/ItemIdDatapd_linp[FLEXIBLE_ARRAY_MEMBER];/*linepointerarray*/}PageHeaderData;typedefPageHeaderData*PageHeader;typedefstructHeapTupleFields{TransactionIdt_xmin;/*insertingxactID*/TransactionIdt_xmax;/*deletingorlockingxactID*/union{CommandIdt_cid;/*insertingordeletingcommandID,orboth*/TransactionIdt_xvac;/*old-styleVACUUMFULLxactID*/}t_field3;}HeapTupleFields;typedefstructDatumTupleFields{int32datum_len_;/*varlenaheader(donottouchdirectly!)*/int32datum_typmod;/*-1,oridentifierofarecordtype*/Oiddatum_typeid;/*compositetypeOID,orRECORDOID*//**Note:fieldorderingischosenwiththoughtthatOidmightsomeday*widento64bits.*/}DatumTupleFields;typedefstructHeapTupleHeaderData{union{HeapTupleFieldst_heap;DatumTupleFieldst_datum;}t_choice;ItemPointerDatat_ctid;/*currentTIDofthisornewertuple(ora*/uint16t_infomask2;/*numberofattributes+variousflags*/uint16t_infomask;/*variousflagbits,seebelow*/uint8t_hoff;/*sizeofheaderincl.bitmap,padding*/bits8t_bits[FLEXIBLE_ARRAY_MEMBER];/*bitmapofNULLs*/}HeapTupleHeaderData;typedefHeapTupleHeaderData*...