Hi, I have carefully traced this part of code and was unable to reproduce what you describe.

If mdb_id2l_search does not find an id in the isc->scopes (lines 782-783, see the excerpt below), the loop just looks id up directly in the dn2id (lines 751-752).

I was also unable to observe that mdb_idscopes could differentiate between paged and non-paged requests, or be affected by the difference. This difference is encapsulated by the caller, mdb_search().

Specifically, if the underlying set of entries changes between page requests, the loop (may) ascend up to "super-root" with zero id. That's exactly what it does for non-paged requests.

And now I am almost sure that the check [if(id == prev)] at line 778 can not succeed, because always compares the parent and child ids coming from the same [child -> parent] record of "dn2id".

Could you, please, take one more look at this part of code? If the check [if(id == prev)] could succeed, could you, please, give a bit more detailed explanation, how may this happen?

Regards, Konstantin.

| 749 while (id) { | 750 if ( !rc ) { | 751 key.mv_data = &id; | 752 rc = mdb_cursor_get( isc->mc, &key, &data, MDB_SET ); ... | 777 /* If we didn't advance, some parent is missing */ | 778 if ( id == prev ) | 779 return MDB_NOTFOUND; | 780 | 781 x = mdb_id2l_search( isc->scopes, id ); | 782 if ( x <= isc->scopes[0].mid && isc->scopes[x].mid == id ) { | 783 if ( !isc->scopes[x].mval.mv_data ) { | 784 /* This node is in scope, add parent chain to scope */

Howard Chu, 28 Oct 2019 20:22 MSK:

If the checks in http://www.openldap.org/devel/gitweb.cgi?p=openldap.git;a=blob;f=servers/sla...

don't find a result, then id doesn't get advanced any further.

This can happen in a pagedResults search when the underlying set of entries changes between page requests.

Konstantin Andreev, 28 Oct 2019 15:03 MSK:

I am contemplating the mdb search mechanics, and puzzled by "missing parent" check in mdb_idscopes():

 | /* If we didn't advance, some parent is missing */
 | if ( id == prev )
 |     return MDB_NOTFOUND;

where "id" and "prev" are parent and child ids that come from the same "UP" ( child -> parent ) record of "dn2id" table. Here is a source code approximation for easier reading:

 | MDB_val key = { sizeof(ID), & id }, data;
 | mdb_cursor_get( "dn2id", key, data, MDB_SET );
 | // reading last sizeof(ID) bytes of data.mv_data
 | ID prev = *(ID *)(data.mv_data + data.mv_size - sizeof(ID));

IIUC, there is no records in "dn2id" where parent and child ids are the same. There is no by construction, except "super-root", where both ids are zeros, but zero id doesn't follow this execution path.

So, how may [id == prev] occur? Could you, please, explain?

The check came from 5a08b661 and 437f21b commits (ITS#7705,#7800 fix ...), I have read both, but they haven't helped either.