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Re: MDB_INTEGERDUP in back-mdb's indexer for attr-tables.

Леонид Юрьев wrote:
Hi, Howard.

I would like to refine my question.

Currently I develop a mdb_chk tool for deep check LMDB-files, like a fsck tool.
It is needed for us, but let this stay aside for now.

On some step I plan to check the size of each key in each DBI with

Initially I assumed - if one of these flags is set, the the length of
all keys must be sizeof(int) or sizeof(long). As will be used the
corresponding comparison functions (mdb_cmp_int, mdb_cmp_long) , which
can handle only keys of such sizes.

But this approach has failed. A dbi-tables created for attr by
mdb_attr_dbs_open() have MDB_DUPSORT|MDB_DUPFIXED|MDB_INTEGERDUP flags
and may contain records with a 5-byte keys. For instance as the

Later you have written that MDB_INTEGERDUP is required.

Now I do not understand how it all works:
  - MDB_INTEGERDUP is set for attr tables.
  - indexer could create a 5-byte keys.
  - mdb-backend set custom comparison function only for MDB_DN2ID table.
  - under debugger I see that md_dcmp is pointed to the default.
  - assert for key-size in default comparators was not failed while "make test".
  - all test are passed without MDB_INTEGERDUP.
  - but you told MDB_INTEGERDUP is necessary

- how and when MDB_INTEGERDUP will have an impact?
- in which cases keys in the table definitely should be sizeof(int) or

MDB_INTGERKEY means the *keys* must be int/long.
MDB_INTEGERDUP means the *values* must be int/long.

When either flag is set, all of the corresponding (keys|values) in the DB must be the same size.

The indexer only uses MDB_INTEGERDUP - it doesn't care what size the keys are, but the values must be (longs in this case).

  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/