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SO close! Happy to help resolve some of these. Would also like to squash it into a single commit with a nice description.
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The clickhouse-cpp library's use of [RAII] and C++ exceptions conflicted
with PostgreSQL's memory management and `PG_TRY`/`setjmp`/`longjmp`
patterns. Analysis of these conflicts lead to the conclusion that
continuing to use the C++ library was unsafe.
Instead, replace the vendored clickhouse-cpp library with the new
headers-only [clickhouse-c] client, also vendored. This package provides
an interface for memory management functions, the `chc_alloc` struct,
mapped here to the Postgres `palloc` family of functions, to ensure
consistent memory handling. It also supports fetching results by block,
rather than all at once, for reduced memory consumption.
This change results in greatly reduced build time without the need to
compile the vendored C++ library, and reduces the size of the resulting
shared library ~75%.
The new library supports all the same features as clickhouse-cpp, but at
a lower level, such that we must handle the conversion of values from
the ClickHouse binary wire format. Most of the conversions are fairly
straightforward, with a few exceptions:
* Encoding and decoding Decimal values
* Encoding parameters requires special quoting and escaping
* Connecting via TCP or TLS requires lower-level socket configuration
However, it also means we no longer rely on clickhouse-cpp's vendored
dependencies (absl, cityhash, lz4, and zstd). Instead, we simply import
the appropriate headers to support compression and encryption and
require the necessary libraries (`liblz4` and `libzstd`). In other
words, no more vendoring aside from the headers.
Take advantage of the consistent use of PostgreSQL's memory management by
creating memory contexts specific to each operation for easy cleanup.
Replace the `src/binary.cpp` and `src/convert.c` files with the
`src/binary` directory with various responsibilities split by `.c` file
for clearer organization:
* `binary.c` - core glue for the driver
* `binary_internal.h` - Private state for the driver
* `connection.c` - TCP with and without TLS connections
* `convert.c` - Binary value conversion, mostly unchanged from
`src/convert.c`
* `decode.c` - Convert ClickHouse wire column values to Postgres
Datums; used for `SELECT`
* `encode.c` - Convert Postgres Datums to ClickHouse binary values and
append to columns; used for `INSERT`
* `insert.c` - Handles `INSERT` process: prepare, insert (flush), and
finalization, along with appending values to ClickHouse columns
* `select.c` - Handles `SELECT` process: simple query, fetching rows
(pump) and cleanup; returns results by block, rather than buffering
all the results at once
Preserve all previous behaviors with three exceptions:
* UInt16 values were previously incorrectly cast to `int16` instead of
`int32`. Fixed here, along with the tests, bringing the behavior in
line with the http driver.
* Bool values cast to `bool`.
* Improved some messages and added additional query context to error
messages.
Update the `Dockerfile` to require `liblz4` and `libzstd`.
Vastly simplify `Makefile`, now that we no longer need to manage a
vendored C++ library that uses `cmake`. Instead we simply add all the C
files to `OBJS` and pull the vendored submodule if it's not already
present (it ships with release packages). We also add the no-longer
vendored `lz4` and `zstd` dependencies to `PG_LDFLAGS`. We also do away
with `clang-format`, which we'd used only for the C++ files, and teach
`pg_bsd_indent` and `clang-tidy` to find the new `*.c` files in
`src/binary`.
Update the GitHub workflow to eliminate caching, since we no longer
build `clickhouse-cpp`, and to install the `lz4` and `zstd`
dependencies. We also remove the separate static and dynamic tests,
since there is just the static build now.
[RAII]: https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization
[clickhouse-c]: https://github.com/ClickHouse/clickhouse-c
Co-authored-by: David E. Wheeler <david.wheeler@clickhouse.com>
This was referenced May 29, 2026
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Resolves #241 and #254.