[GitHub] [tinkerpop] simonz-bq commented on pull request #1465: TINKERPOP-2486 Fix load balancing across connections

[GitBox <gi...@apache.org>]

simonz-bq commented on pull request #1465:
URL: https://github.com/apache/tinkerpop/pull/1465#issuecomment-919600535


   I updated the connection pool logic a bit to be simpler and to solve the load balancing issues due to race conditions.
   
   In my opinion the change seems reasonable but there may be a side effect that I haven't considered or figured out.
   
   Aside from the load balancing issues, the old and new logic work as follows for getting a connection:
   
   1. Grab the least used connection
   2. If no connection could be returned, wait for one to be available
   3. If the least used connection's borrow count is higher than `maxSimultaneousUsagePerConnection`, consider making a new connection if the pool is not full. **Even if `maxSimultaneousUsagePerConnection`, this least used connection is still considered a valid connection to return**
   4. If the least used connection's borrow count is higher than `maxSimultaneousUsagePerConnection` AND the least used connection has reached it's maximum processes, wait for one to be available
   5. Else, return the least used connection
   
   The old logic allowed a connection to be grabbed even if `maxSimultaneousUsagePerConnection` was exceeded, and only deemed it invalid if also the maximum processes was reached.
   
   New:
   
   1. Grab the least used connection that is below the `maxSimultaneousUsagePerConnection` count
   2. Increment the borrow count, and if it now reaches `maxSimultaneousUsagePerConnection`, consider creation of a new connection
   3. If a least used connection could not be grabbed, then wait for one to be available


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