SpriCoder opened a new pull request, #17800:
URL: https://github.com/apache/iotdb/pull/17800
## Summary
This PR improves the C++ client (`iotdb-client/client-cpp`) along three axes
— concurrency, read/write performance, and safety/correctness. It is split into
four logically separate commits.
### 1. Thread-safe `SessionPool` (new feature)
A single `Session` is not safe to use from multiple threads concurrently (it
owns one Thrift transport/client). Previously the C++ client had no pooling,
forcing callers to either serialize all requests through one session or
hand-roll connection management.
- New `SessionPool` + `SessionPoolBuilder` lend each `Session` to exactly
one borrower at a time and reclaim it afterwards, so many application threads
can share a bounded set of connections without external locking.
- `getSession()` returns an RAII `PooledSession` handle that returns the
session to the pool on scope exit and works with any `Session` method; a
generic `execute([](Session&){...})` plus convenience wrappers (`insertTablet`,
`insertRecord`, `executeQueryStatement`, …) cover common operations.
- New sessions are constructed **outside** the pool lock so a handshake
never blocks other borrowers; `getSession()` blocks up to a configurable
timeout when the pool is exhausted.
- Query results are returned as a `PooledSessionDataSet` that keeps the
session leased until the result set is fully read — necessary because
`SessionDataSet` lazily fetches further blocks over the same connection.
Sessions that raise `IoTDBConnectionException` are evicted instead of recycled.
### 2. Enable RPC compression that was silently ignored (performance)
`Session::open(bool enableRPCCompression)` and the builder's
`enableRPCCompression` flag were never propagated to `SessionConnection`, whose
flag was hardcoded to `false`, so the compact Thrift protocol never took
effect. The flag is now threaded from the builder/`open()` into both the data
`SessionConnection` and the node-discovery `NodesSupplier` client, reducing
bytes on the wire for both reads and writes.
### 3. Safety / correctness hardening
- `Tablet::addValue` formatted out-of-range diagnostics with `sprintf` into
a fixed 100-byte stack buffer; switched to `snprintf` bounded by
`sizeof(buffer)` to remove the overflow risk.
- `MyStringBuffer::putOrderedByte` used `str.assign` on big-endian hosts,
which overwrote the whole buffer on every numeric write and corrupted
previously serialized content; changed to `str.append` to match the
little-endian path.
## Commits
1. Wire RPC compression flag through Session to its connections
2. Use snprintf for Tablet bounds-check error messages
3. Append big-endian bytes in MyStringBuffer instead of overwriting
4. Add thread-safe SessionPool to the C++ client
## Test plan
- [x] All changed/new sources compile cleanly against the project's
Thrift/Boost headers (`g++ -std=c++11 -fsyntax-only`, 0 errors); new code
conforms to the repo `.clang-format` (2-space, 100-col).
- [ ] Run the C++ client integration tests against a live IoTDB on
`127.0.0.1:6667` (`session_tests`), including the new `[sessionPool]` cases:
basic borrow/insert/query, concurrent writers, and exhaustion-timeout. These
require a running server and were not executed in the authoring environment.
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