ArangoDB 键/值 Model：值最大大小

Question

With regard to the Key/Value model of ArangoDB, does anyone know the maximum size per Value? I have spent hours searching the Internet for this information but to no avail; you would think that this is a classified information. Thanks in advance.

Answer 1

The answer depends on different things, like the storage engine and whether you mean theoretical or practical limit.

In case of MMFiles, the maximum document size is determined by the startup option wal.logfile-size if wal.allow-oversize-entries is turned off. If it's on, then there's no immediate limit.

In case of RocksDB, it might be limited by some of the server startup options such as rocksdb.intermediate-commit-size , rocksdb.write-buffer-size , rocksdb.total-write-buffer-size or rocksdb.max-transaction-size .

When using arangoimport to import a 1GB JSON document, you will run into the default batch-size limit. You can increase it, but appears to max out at 805306368 bytes (0.75GB). The HTTP API seems to have the same limitation ( /_api/cursor with bindVars).

What you should keep in mind: mutating the document is potentially a slow operation because of the append-only nature of the storage layer. In other words, a new copy of the document with a new revision number is persisted and the old revision will be compacted away some time later (I'm not familiar with all the technical details, but I think this is fair to say). For a 500MB document is seems to take a few seconds to update or copy it using RocksDB on a rather strong system. It's much better to have many but small documents.