Environment variables

Diagnostic / opt-in knobs the driver reads at runtime. Every flag here defaults to "off" and is meant for development, performance triage, or ad-hoc protocol debugging — production callers should leave them unset.

Naming convention. Knobs that are meaningful for every Arpeio ADBC driver (ArrowTDS/SQL Server, ArrowFEBE/PostgreSQL, ArrowTTC/Oracle, …) use the shared ARPEIO_ADBC_* prefix, so one variable configures the whole family in a process. Knobs specific to one driver/protocol use that driver's ARROW<CODE>_* prefix (here, ARROWTDS_*). Each variable lives in exactly one namespace — there is no per-driver override of a shared variable. The mandatory licence lookup also uses the shared prefix (ARPEIO_ADBC_LICENCE[_FILE], see Licensing).

A truthy value is anything non-empty whose first character is not '0', unless the table notes a stricter test (e.g. ARROWTDS_USE_TDS_RPC specifically matches 1 / true / TRUE / yes).

Read path (SELECT)

Variable	Effect
`ARPEIO_ADBC_READ_TIMING`	Per-batch wall-time breakdown on the SELECT stream. Emits one `[TDS READ]` line per batch (`recv_ms`, `decode_ms`, `writer_wait_ms`, `recv_kb`, `cpu_user_ms`, `cpu_krn_ms`) plus a `[TDS READ SUMMARY]` at stream release that adds `busy_ms` (wall time the reader thread was runnable, i.e. not parked in `writer_wait`) and `alloc=` (the column-buffer allocator backend, see `ARPEIO_ADBC_ALLOCATOR`). Use this to decide whether the bottleneck is the wire (`recv_ms`), the row decoder (`decode_ms`), or downstream backpressure (`writer_wait_ms`) — and, when a stage is slow, whether the thread was blocked (`busy_ms` ≫ `cpu_user_ms + cpu_krn_ms`: waiting on locks/pages/preemption) or genuinely out of CPU (the two are close).
`ARROWTDS_TDS_READ_DEBUG`	Verbose per-token trace in the native TDS read path: ENVCHANGE token type/length, RPC stream framing, parser state transitions. Very chatty — only useful when triaging a wire-protocol bug.
`ARROWTDS_VECTOR`	Kill-switch for SQL Server 2025 native vector transport. Default on: LOGIN7 offers `FEATUREEXT_VECTORSUPPORT`, and a 2025 server then returns `VECTOR(n)` columns as Arrow `fixed_size_list<float32>[n]`. Set to a false-y value (`0`, `off`, `no`, `false`) to stop offering the feature, in which case the server falls back to exposing vectors as `varchar(max)` JSON (→ `utf8`). Older servers ignore the unknown feature regardless. Read at login.

Write path (BULK INSERT / `adbc_ingest`)

Variable Effect

ARPEIO_ADBC_QUIET Suppresses the bulk path's stderr output: the [TDS TIMING] summary printed after every ingest (begin / encode+send / wait_done / total / rows / server_rows / sub_batches) and the encryption-downgrade and client/server row-count-mismatch warnings. Default is visible; any non-empty value not starting with 0 mutes them. Used by the validation suite to keep test output clean, and by shared-logging environments that must not leak server/topology details.

Variable	Effect
`ARPEIO_ADBC_QUIET`	Suppresses the bulk path's stderr output: the `[TDS TIMING]` summary printed after every ingest (`begin / encode+send / wait_done / total / rows / server_rows / sub_batches`) and the encryption-downgrade and client/server row-count-mismatch warnings. Default is visible; any non-empty value not starting with `0` mutes them. Used by the validation suite to keep test output clean, and by shared-logging environments that must not leak server/topology details.

Memory / allocator

Variable Effect

ARPEIO_ADBC_ALLOCATOR Selects the allocator backing the row decoder's Arrow column buffers: mimalloc (default when the driver is built with ARROWTDS_WITH_MIMALLOC, which release builds are) or system (libc malloc — the escape hatch if the mimalloc-backed buffers misbehave). Read once, at the first column-buffer allocation; the choice is stable for the process lifetime and is reported as alloc= in the [TDS READ SUMMARY] line. system always works; mimalloc is silently ignored when not compiled in.

Variable	Effect
`ARPEIO_ADBC_ALLOCATOR`	Selects the allocator backing the row decoder's Arrow column buffers: `mimalloc` (default when the driver is built with `ARROWTDS_WITH_MIMALLOC`, which release builds are) or `system` (libc `malloc` — the escape hatch if the mimalloc-backed buffers misbehave). Read once, at the first column-buffer allocation; the choice is stable for the process lifetime and is reported as `alloc=` in the `[TDS READ SUMMARY]` line. `system` always works; `mimalloc` is silently ignored when not compiled in.

Statement execution

Variable	Effect
`ARROWTDS_USE_TDS_RPC`	Route no-rowset DML / DDL through the `sp_executesql` RPC token instead of the default `SQLBATCH` token. Phase 7a opt-in — used during the RPC migration to A/B the two paths. Accepts `1`, `true`, `TRUE`, `yes`.

Licence

Unlike the diagnostic flags above, these configure the mandatory licence check the driver runs at connection time (see Licensing for the full resolution order and the equivalent arpeio.adbc.license* database options). They are read only if those options are not set.

Variable	Effect
`ARPEIO_ADBC_LICENCE`	The licence blob, inline. Used when neither the `arpeio.adbc.license` nor `arpeio.adbc.license_file` option is set.
`ARPEIO_ADBC_LICENCE_FILE`	Path to a `.lic` file. Checked after `ARPEIO_ADBC_LICENCE`; if neither this nor the options are set, the driver falls back to an `arpeio_adbc.lic` file next to the driver binary.

Build-time overrides

Read once during build, not at runtime.

Variable	Effect
`ARROWTDS_NATIVE_ARCH`	`ON` (default) compiles the ADBC driver with `-march=native`. Override `OFF` for portable-binary distributors.

C# loader and parquet-export shim env vars (ARROWTDS_DRIVER_PATH, ARROWTDS_SHIM_PATH, ARROWTDS_VCPKG_DLLS, ARROWTDS_EXPORT_TIMING, ARROWTDS_USE_WRITE_TABLE, ARROWTDS_PARQUET_VERSION, …) moved with the parquet_export tool to adbc-file-export.

Read path (SELECT)​

Write path (BULK INSERT / adbc_ingest)​

Memory / allocator​

Statement execution​

Licence​

Build-time overrides​