Logic behind import and export

Question

HI all
Can anybody explain
1 What actually happend at oracle level while taking export and import?

Answer 1

There is no explanation as it is not documented what internally happens with export and import.
The EXPORT puts together the information about the objects imported in way that IMPORT understands and is able to generate DDLs to recreate those objects with data using the information in the export dump file.
I created a table TT and added three rows to it. Then I exported this table TT using export utility. Following are the contents of the dump file.
$ strings myDump.dmp
EXPORT:V10.02.01
USCOTT
RTABLES
8192
myDump.dmp
#C##
#C##
+00:00
BYTE
UNUSED
INTERPRETED
DISABLE:ALL
METRICST
TABLE "TT"
CREATE TABLE "TT" ("ID" NUMBER)  PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 STORAGE(INITIAL 65536 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT) TABLESPACE "USERS" LOGGING NOCOMPRESS
INSERT INTO "TT" ("ID") VALUES (:1)
METRICSTreferential integrity constraints
METRICET 3
METRICSTtriggers
METRICET 3
METRICSTbitmap, functional and extensible indexes
METRICET 3
METRICSTposttables actions
METRICET 3
METRICSTPost-inst procedural actions
METRICET 3
METRICETG0
EXIT
EXITI have used the strings command which shows non binary contents of the file. As you can see above the CREATE TABLE is recorded in the dump file by EXP, and one INSERT INTO statement with the bind variable in the values clause. So that seems the IMP utility repeats the INSERT INTO statement 3 times because there are three rows in the table and every time it changes the bind :1 with the real row data, which may have been stored in the dump file as binary.
Then I imported this dump file back using the IMP utility.
$ imp scott/tiger full=y ignore=yes
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
IMP-00002: failed to open expdat.dmp for read
Import file: expdat.dmp > myDump.dmp
Export file created by EXPORT:V10.02.01 via conventional path
import done in US7ASCII character set and AL16UTF16 NCHAR character set
import server uses WE8ISO8859P1 character set (possible charset conversion)
. importing SCOTT's objects into SCOTT
. importing SCOTT's objects into SCOTT
. . importing table                           "TT"          3 rows imported
Import terminated successfully with warnings.