alamb commented on code in PR #4918:
URL: https://github.com/apache/arrow-rs/pull/4918#discussion_r1362745234
##########
object_store/src/aws/copy.rs:
##########
@@ -39,12 +39,64 @@ pub enum S3CopyIfNotExists {
///
/// [`ObjectStore::copy_if_not_exists`]:
crate::ObjectStore::copy_if_not_exists
Header(String, String),
+ /// The name of a DynamoDB table to use for coordination
+ ///
+ /// Encoded as `dynamodb:<TABLE_NAME>` ignoring whitespace
+ ///
+ /// This will use the same region, credentials and endpoint as configured
for S3
+ ///
+ /// ## Limitations
+ ///
+ /// Only conditional operations, e.g. `copy_if_not_exists` will be
synchronized, and can
+ /// therefore race with non-conditional operations, e.g. `put`, `copy`, or
conditional
+ /// operations performed by writers not configured to synchronize with
DynamoDB.
+ ///
+ /// Workloads making use of this mechanism **must** ensure:
+ ///
+ /// * Conditional and non-conditional operations are not performed on the
same paths
+ /// * Conditional operations are only performed via similarly configured
clients
+ ///
+ /// Additionally as the locking mechanism relies on timeouts to detect
stale locks,
+ /// performance will be poor for systems that frequently rewrite the same
path, instead
+ /// being optimised for systems that primarily create files with paths
never used before.
+ ///
+ /// ## Locking Protocol
+ ///
+ /// The DynamoDB schema is as follows:
+ ///
+ /// * A string hash key named `"key"`
+ /// * A numeric [TTL] attribute named `"ttl"`
+ /// * A numeric attribute named `"generation"`
+ ///
+ /// The lock procedure is as follows:
+ ///
+ /// * Error if file exists in S3
+ /// * Create a corresponding record in DynamoDB with the path as the
`"key"`
+ /// * On Success: Create object in S3
+ /// * On Conflict:
+ /// * Periodically check if file exists in S3
+ /// * After a 60 second timeout attempt to "claim" the lock by
incrementing `"generation"`
+ /// * GOTO start
+ ///
+ /// This is inspired by the [DynamoDB Lock Client] but simplified for the
more limited
+ /// requirements of synchronizing object storage.
+ ///
+ /// The major changes are:
+ ///
+ /// * Uses a monotonic generation count instead of a UUID rvn
Review Comment:
I was thinking collision of concurrent writers (different processes)
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