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Use Kyle's feedback to better explain consistency model about txn ord…
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…ering.
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@manishrjain @danielmai
manishrjain authored and danielmai committed Feb 21, 2020
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3 changes: 2 additions & 1 deletion wiki/content/design-concepts/index.md
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Expand Up @@ -28,7 +28,8 @@ them in a Raft group.
- The transactions are cluster-wide (not key-only, or any other "crippled" version of them).
- Transactions are lockless. They don't block/wait on seeing pending writes by uncommitted transactions. Zero would choose to commit or abort them depending on conflicts.
- Transactions are based on Snapshot Isolation (not Serializable Snapshot Isolation), because conflicts are determined by writes (not reads).
- Dgraph supports cluster-wide Linearizable Reads. Any commits at timestamp Tc are guaranteed to be seen by a following read at timestamp Tr (by any client), if Tr > Tc.
- Dgraph hands out monotonically increasing timestamps (for transactions). Ergo, if any transaction Tx1 commits before Tx2 starts, then Ts_commit(Tx1) < Ts_start(Tx2).
- Any commit at Tc are guaranteed to be seen by a read at timestamp Tr by any client, if Tr > Tc.
- All reads are snapshots across the entire cluster, seeing all previously committed transactions in full.

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