Search indexer logs problems, MAPI error or timeout

I’m currently tracking down a problem with the search indexer, which logs the following after being restarted (in debug mode):

2018-05-11 11:47:21,702 - index0 - DEBUG - store 70BE20DDCD354C668815C070B9294347, folder 21: new/updated document with entryid 0000000070BE20DDCD354C668815C070B9294347010000000500000030C0A96A41E9C44987A9E6C90AECDBD500000000, sourcekey E145B78F5634408F9A731E5AA829B812C58C0B000000, docid 1357094
2018-05-11 11:47:21,722 - index0 - DEBUG - store 70BE20DDCD354C668815C070B9294347, folder 21: new/updated document with entryid 0000000070BE20DDCD354C668815C070B9294347010000000500000099F5477896A8394785FC4F6ADE628B5200000000, sourcekey E145B78F5634408F9A731E5AA829B812AD8A0B000000, docid 1356068
2018-05-11 11:47:21,733 - index0 - DEBUG - store 70BE20DDCD354C668815C070B9294347, folder 21: new/updated document with entryid 0000000070BE20DDCD354C668815C070B9294347010000000500000091D76A02D417E348BD0BE4CEF9D4474E00000000, sourcekey E145B78F5634408F9A731E5AA829B812F3880B000000, docid 1355144
2018-05-11 11:47:21,754 - index0 - WARNING - Received a MAPI error or timeout (error=0x80040115, retry=0/5)
2018-05-11 11:47:22,180 - index0 - WARNING - Received a MAPI error or timeout (error=0x8004010f, retry=1/5)
2018-05-11 11:47:22,995 - index0 - WARNING - Received a MAPI error or timeout (error=0x8004010f, retry=2/5)
2018-05-11 11:47:24,616 - index0 - WARNING - Received a MAPI error or timeout (error=0x8004010f, retry=3/5)
2018-05-11 11:47:27,839 - index0 - WARNING - Received a MAPI error or timeout (error=0x8004010f, retry=4/5)
2018-05-11 11:47:34,268 - index0 - WARNING - Received a MAPI error or timeout (error=0x8004010f, retry=5/5)
2018-05-11 11:47:40,675 - index0 - ERROR - Too many retries, skipping change

This corresponds with the following kopano-server logs, also on debug level.

Fri May 11 14:03:56 2018: [error  ] Previous message logged 3 times
Fri May 11 14:03:56 2018: [debug  ] Accepted incoming connection from file:///var/run/kopano/server.sock
Fri May 11 14:03:56 2018: [error  ] ECDatabaseAttachment::LoadAttachmentInstance(): no row returned
Fri May 11 14:03:56 2018: [error  ] SerializeObject failed with error code 0x80000007 for object 1353495
Fri May 11 14:03:56 2018: [debug  ] gSOAP error on processing request: SOAP_FATAL_ERROR
Fri May 11 14:03:57 2018: [error  ] Error while connecting to search on "file:///var/run/kopano/search.sock"

Can somebody help me to track down the problem?

And is there a documentation of the database structure? I’m quite sure there is a problem with an attachment at a calendar item (because search indexes my calendar at this moment), but I don’t know how to identify it.

OK, to answer myself (giyf!) … the database structure is documented at https://github.com/Kopano-dev/kopano-core/blob/master/doc/Database_structure.md

I’m out of office for a few days, so I can work on this issue when I’m back.