Reading deleted records - PageHeader v3 - Mailing list pgsql-hackers

<div class="Section1"><p class="MsoNormal">Hi, <p class="MsoNormal"> <p class="MsoNormal">So first I’m a pgsql hacker
newbieand I’ve been reading up on the storage structure: <p class="MsoNormal"><a
href="http://www.postgresql.org/docs/8.2/interactive/storage-page-layout.html">http://www.postgresql.org/docs/8.2/interactive/storage-page-layout.html</a><p
class="MsoNormal"> <pclass="MsoNormal">I’m trying to recover deleted records from a page file (postgresql 8.2) : i.e.
base/dbId/20132<pclass="MsoNormal"> <p class="MsoNormal">I am able to successfully read all the header data I need
(PageHeaderData,ItemIdData , HeapTupleHeaderData) <p class="MsoNormal">but I hit a wall when I try to start reading
userdata. <p class="MsoNormal"> <p class="MsoNormal">This has helped:<p class="MsoNormal"><a
href="http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/postgres.h?rev=1.77;content-type=text%2Fplain">http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/postgres.h?rev=1.77;content-type=text%2Fplain</a><p
class="MsoNormal"> <pclass="MsoNormal">I’ve read and understood fairly well how varlena structures are stored (plain,
compressed,external/toast) but so far I can’t seem to read a plain inline value.<p class="MsoNormal">I think part of my
problemis I haven’t really understood what ‘Then make sure you have the right alignment’ means. <p
class="MsoNormal"> <pclass="MsoNormal">My approach currently is:<p class="MsoNormal">After reading HeapTupleHeaderData
(23bytes), I advance another 4 bytes (hoff) and try to read a 32 bit integer (first attribute).<p class="MsoNormal"> <p
class="MsoNormal">Iam expecting to get an integer value 1 but I get 512 .<p class="MsoNormal"> <p class="MsoNormal">Am
Idoing this wrong? <p class="MsoNormal">Could someone point me to the pgsql code pieces I should be looking at? <p
class="MsoNormal"> <pclass="MsoNormal">If useful, this is the information I have before reading the ‘user data’:<p
class="MsoNormal"> <pclass="MsoNormal">object(PostgreSQL_HeapTupleHeaderData)#14 (7) {<p class="MsoNormal"> 
["xmin"]=><pclass="MsoNormal">  string(5) "13824"<p class="MsoNormal">  ["xmax"]=><p class="MsoNormal"> 
string(1)"0"<p class="MsoNormal">  ["cid"]=><p class="MsoNormal">  string(1) "0"<p class="MsoNormal"> 
["ctid"]=><pclass="MsoNormal">  object(PostgreSQL_ItemPointerData)#16 (2) {<p class="MsoNormal">   
["blockId"]=><pclass="MsoNormal">    string(1) "0"<p class="MsoNormal">    ["posId"]=><p class="MsoNormal">   
int(0)<pclass="MsoNormal">  }<p class="MsoNormal">  ["infomask2"]=><p class="MsoNormal">  int(0)<p
class="MsoNormal"> ["infomask"]=><p class="MsoNormal">  int(2)<p class="MsoNormal">  ["hoff"]=><p
class="MsoNormal"> int(4)<p class="MsoNormal">}<p class="MsoNormal">object(PostgreSQL_Attribute)#7 (6) {<p
class="MsoNormal"> ["name"]=><p class="MsoNormal">  string(7) "book_id"<p class="MsoNormal">  ["relid"]=><p
class="MsoNormal"> int(20132)<p class="MsoNormal">  ["len"]=><p class="MsoNormal">  int(4)<p class="MsoNormal"> 
["num"]=><pclass="MsoNormal">  int(1)<p class="MsoNormal">  ["ndims"]=><p class="MsoNormal">  int(0)<p
class="MsoNormal"> ["align"]=><p class="MsoNormal">  string(1) "i"<p class="MsoNormal">}<p
class="MsoNormal">array(1){<p class="MsoNormal">  ["book_id"]=><p class="MsoNormal">  int(512)<p
class="MsoNormal">}</div>