Hello,
Firstly I want to thank you all for the fast answers and the support.
I've somo other questions:
0) What is the structure of a heap table in memory? How infos about columns are stored and
how rows are memorized? And when an existent
table is opened, from where all its infos are retreived?
1) I found that in the creation of a heap table it seems that just infos about keys are
stored: in fact in the HP_CREATE_INFO struct no
info about other fields are utilized. The function heap_create() in hp_create.* takes as
parameters this HP_CREATE_INFO and just infos
about keys and record length. Where are things about non-key fields and how are managed?
And where the fixed length of rows for a table is
setted?
2) If I don't misunderstand, in the function heap_create() the memory blocks for the table
rows are initialized with the instruction
"init_block(&share->block, reclength + 1, min_records, max_records)", in which
"reclength" comes from the TABLE_SHARE (SQL layer): now this
parameter, when in a table there are blobs, computes the record length where the length of
blob field is sizeof(pack_length)+sizeof(char*)
or sizeof(pack_length)+pack_length? Because in the first case, reclength would be the same
for my heap tables with blobs, but in the second
one, I may calculate a new_reclength where I shoul subtract the pack_length for all the
blobs and add something like num_of_blobs*sizeof
(char*)...
3) I analyzed mi_dynrec.c and the suggested function _mi_rec_pack(): thanks to this, I
understood how blob fields are managed in isam
storage engine. A thing that I'd have explained is the real meaning of the word/verb pack
in this context, which seems to be linked with
dynamic rows. What does it mean the hermetic comment /* Pack a record. Return new
reclength */. I interpredet it as: copy in record[0] the
pack_length and the pack itself, but I'm not sure.
I'm trying to start modifications, but I want to be sure that I don't make stupid
mistakes...
Thanks again.
Emanuele Conti
Senior Student at University ROMA TRE
Department of Informatics and Automation
ROME, Italy (matr. 251318)
Mob: +39 328 2681070
Home: +39 06 39741124
e-mail: emanuele.conti@stripped
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