Daml is a smart contract language based on declarative and functional paradigms. It is implemented on several different distributed ledgers including blockchains (Besu, Sawtooth, QLDB, et al) as well as traditional databases (Postgres). From the perspective of the Daml contract developer there is no difference between these platforms and the APIs presented by Daml are identical across all ledgers given the same Daml version. Fully documenting Daml is beyond the scope of this documentation, but excellent and thorough documentation may be found at https://daml.com.
Notably useful pages within the Daml site to look at are:
Across all of our Daml implementations there are a few recurring infrastructure themes which are usefully discussed without respect to a particular ledger.
Time, "ledger time", or "record time" is a significant feature in all Daml ledger implementations. All of the ledgers we support have a running "wall clock" this clock is guaranteed to monotonically increase on every ledger, and corresponds to but is not necessarily exact when compared to an high accuracy time service.
In blockchain based ledgers the ledger time is a consensus mediated time that can be agreed upon by all validating nodes in the network.
In centralized ledgers (such as Postgres or currently QLDB) this time is based on the machine time of the servers running on the node.
Regardless the time is always guaranteed to monotonically increase with respect to the ledger records.
Caching and Package Warm-up¶
Daml contracts are effectively instances of templates within packages loaded in to the ledger. For a given process running the Daml runtime engine, the first time a package is uploaded, or the first time a contract instance of a template is exercised (whichever happens first over the lifetime of the process), the template code is loaded into memory and compiled. This compiled code is then cached and kept in memory. This "warm-up" behavior will be repeated on any process that is restarted. This can have varying effects, up to and including producing GRPCIOTimeouts on calls while the templates are being compiled.
Certain of the ledger implementations have some hints and pre-loading to mitigate this behavior but it is a good idea to bear it in mind while developing you're application.
Access to a Daml ledger is accomplished via one of two protocols: GRPC, or via the HTTP based JSON-API.
While it is customizable in all of our deployments, the default for BTP
deployments is to place the GRPC endpoint on port
39000 and the JSON-API port
8080. In each case the access is governed via the use of JWT tokens.
Daml ledger API access and authorization is controlled through the use of JWT tokens(discussed in details here). These may be