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dbprint

Redshift

Terminal window
$ pip install 'dbprint[redshift]'

The extra carries redshift-connector>=2.1. Absent driver: redshift-connector is not installed. Install dbprint with the [redshift] extra: \pip install dbprint[redshift]`.A failed connection:could not connect to Redshift at :/ as : . The connection opens with autocommit = True`; the adapter applies no session-level read-only setting.

Fully-qualified names are schema.table.

Privileges

CREATE USER dbprint_ro PASSWORD '...';


GRANT USAGE ON SCHEMA seedbank TO dbprint_ro;
GRANT SELECT ON ALL TABLES IN SCHEMA seedbank TO dbprint_ro;


-- The one grant that matters: without it, size-gated rules silently do not apply.
GRANT SELECT ON svv_table_info TO dbprint_ro;
PrivilegeOnNeeded for
USAGEeach schema profiledreaching anything inside it
SELECTeach table and materialized view profiledDDL and statistics
SELECTsvv_table_infothe row-count estimate every size-gated rule reads
TEMP (via PUBLIC)the databasethe sampled-table copy — every user already holds this through PUBLIC membership; it is not CREATE ON SCHEMA
—svv_redshift_tables, svv_redshift_columns, stv_mv_infoneed nothing beyond connecting — they self-filter to the caller's own objects

Read this one: svv_table_info is superuser-only by default

SVV_TABLE_INFO is visible only to superusers, and GRANT SELECT ON svv_table_info TO <user> is what permits an ordinary user to query it. GRANT ROLE sys:monitor is a second route to the same access. SYSLOG ACCESS UNRESTRICTED is not a substitute — it does not open superuser-visible system views.

Without that grant, estimate_row_count catches the failure and returns -1 for every table, silently: the run warns no row-count estimate for '<fqn>'; rules carrying \min_rows` or a `max_rows_scanned` ceiling do not apply to it, but nothing else in the run tells a reader that the whole size-gating system just went dark. An empty table is missing from SVV_TABLE_INFO` entirely, rather than reported as zero, so its absence there is not itself a sign of a missing grant.

Sampling

ConstructRANDOM() < p in a wrapping subquery
Seededno — RANDOM() carries no seed at all on Redshift
looks_like sub-drawoversamples with RANDOM(); the distinct set is hash-ordered either way

Because the fraction cannot be seeded, coherence across a sampled table depends entirely on the materialized copy below — there is no population-level fallback guarantee the way duckdb or PostgreSQL have.

When dbprint writes

Only one thing makes dbprint write, and only under one condition: materialize_sample is on by default, and it fires only for a table narrowed to a fraction of its rows. A fraction has two sources — a rule's sample, and a max_rows_scanned ceiling resolving against the table's size, which is legal at connection and defaults level as well as inside a rule. A project that narrows nothing, which is what dbprint init scaffolds, never writes. A filter is a predicate rather than a fraction and never materializes.

Where it does fire, the drawn rows are copied once into a session-lifetime temporary table - CREATE TEMPORARY TABLE <name> AS SELECT * FROM (SELECT * FROM <table> WHERE RANDOM() < p) AS dbprint_scoped, evaluating RANDOM() exactly once — and every statistics statement for that table reads the copy.

materialize_sample: false never falls back on Redshift: SAMPLE_FALLBACK_COHERENT is false here, so a sample-scoped table with the write disabled, or a refused write, is refused outright rather than degrading:

table 'seedbank.germination_trial': connection 'primary' (redshift) sets
materialize_sample: false, and this adapter's per-statement sampling construct cannot be
seeded into agreement across statements. Set materialize_sample: true for this connection,
or narrow with a filter instead of a sample fraction.

Identifiers

Both path segments are lowercased for the FQN, and the rule check refuses two objects whose physical spellings differ only by case with case-collides-with-<other>. A mixed-case column keeps its own spelling in physical_name; addressing one for the looks_like draw re-reads the catalog's spelling under enable_case_sensitive_identifier, raising no column named <name> (case-insensitive) on <fqn> when there is no match.

What it cannot deliver

  • indexes — always empty. No index concept exists on Redshift.
  • depends_on on a late-binding view — always absent. A late-binding view has no pg_rewrite entry, and the code drops the unresolved row rather than let it collapse into "resolved, reads nothing" — so such a view is missing from the dependency map entirely.
  • Row-count estimate without the svv_table_info grant — see "Read this one" above.
  • Foreign key on_delete / on_update — always NO ACTION. The FK grammar Redshift exposes carries no referential-action slot.

is_nullable on a column has a documented blank third state; only an explicit NO / FALSE / F makes the NOT NULL claim.

Reference