Recently (the past few years actually) we’ve been experiencing that Mercurial has problems scaling to it’s activity. Here are some statistics for example: 24550 Mercurial heads (this is reset every few months) Head count correlated with the degraded performance 4.3 GB in size, 203509 files without a working copy One of the methods we’re attempting is to modify try so that each push is not a head, but is instead a bundle that can be applied cleanly to any [mozilla-central](https://hg.
The Mercurial developers were concerned about race conditions and concurrent write/reads causing service inconsistency between hosts. This became evident when stale file handles started appearing in our apache logs. An extension we wrote (pushlog) was also being served off of NFS. This is a problem not because we have multiple hosts writing at once, but because the file is kept in memory for the lifetime of the hgweb-serving WSGI process, and we’ve experienced that sometimes requests to the pushlog can be served old information.