[GEODE-7692] Sort PdxTypeToTypeIdMap by hash.

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: native client
• Assignee: Unassigned
• Reporter: Matthew Reddington
• Created: 13/Jan/20 18:18
• Updated: 13/Jan/20 18:18

Description

PdxTypeToTypeIdMap sorts its keys by "class name", which is not unique and is the root cause of all our Pdx troubles. The key is a PdxType, and the sorting order should be determined by a hash of the class name and PdxTFieldTypes. Use boost::hash_combine to hash the fields and then hash the field hashes.

• This hashing strategy is called a Merkle Tree.
• hash_combine relies on a magic number where each bit has a random chance of being 0 or 1. This has the effect of spreading consecutive values far apart. Their random number is the multiplicative inverse of phi - imaginary numbers are good for this, according to my research.

You can't hash the type ID because this is always 0 for local types, and it's also 0 for remote types for which we haven't yet received the type id from the server, or we have constructed a PdxType to perform a lookup to find the type id in the PdxTypeRegistry, which uses this very map for type id lookup.