This document describes errors you might encounter when you generate a ScaNN
index. Examples of errors and recommended fixes are also provided.
List of errors
The following a list of errors that are generated when you try to create a
ScaNN
index. You can disable generation of these errors and continue to generate
the index. For more information, see Enforce index creation and suppress errors.
ERROR: Cannot create ScaNN index with empty table
Error message
When you try to generate an index on a table with no data or try to truncate a
table with a ScaNN
index generated on it, the following error occurs:
ERROR: Cannot create ScaNN index with empty table. Once the table is populated
with data, create the index. See documentation to bypass this validation.
Sample queries that cause the error
Query Example A
create table t1 (a INT, b VECTOR(512)); CREATE TABLE create index on t1 using ScaNN(b cosine) with (num_leaves = 10, quantizer = 'sq8');
Query Example B
truncate t1;
Recommended fix
Make sure that your table is populated with embedding vectors before you generate a ScaNN
index.
ERROR: Cannot create ScaNN index
Error message
When you try to generate an index on a table with few rows populated, the following error occurs:
Cannot create ScaNN index, error: INVALID_ARGUMENT: Number of row (5) must be
larger than (1000).
Sample query that causes the error
create table t1 (a INT, b VECTOR(512));
CREATE TABLE
insert into t1 select (random()*1e9)::int, random_vector(512) from generate_series(1, 5);
INSERT 0 5
create index on t1 using scann(b cosine) with (num_leaves = 100, quantizer = 'sq8');
Recommended fix
Ensure that your table is populated with embedding vectors before you generate a
ScaNN
index. We recommend that the number of rows in the table are greater
than the value defined in the num_leaves
parameter.
ERROR: Cannot create ScaNN index on parent partition table.
Error message
If you have created partitioned tables from a parent table, then creating a ScaNN index on the parent table generates the following error:
ERROR: Cannot create ScaNN index on parent partition table. Create ScaNN
indexes on the child tables instead. See documentation to bypass this
validation.
Sample query that causes the error
create table t1 (a INT, b VECTOR(512)) partition by range(a);
CREATE TABLE
CREATE TABLE t1_one_ten PARTITION of t1 for values from (1) to (10);
CREATE TABLE
insert into t1_one_ten select (random()*1e9)::int, random_vector(512) from generate_series(1, 100);
INSERT 0 100
CREATE TABLE t1_eleven_twenty PARTITION of t1 for values from (11) to (20);
CREATE TABLE
insert into t1_eleven_twenty select (random()*1e9)::int, random_vector(512) from generate_series(1, 100);
INSERT 0 100
create index on t1 using scann(b cosine) with (num_leaves = 10, quantizer = 'sq8');
Recommended fix
You can't generate a ScaNN
index on the parent table of a partitioned table.
You must generate the ScaNN
indexes on the partitioned table.
Enforce index creation and suppress errors
You can enforce AlloyDB to generate an index and suppress errors. Before allowing index generation with this method, consider the following implications:
- Since the index is trained on less or no data, centroids learn on zero data leading to bad recall.
- The write performance to the database might also be slow.
To force index generation, complete the following:
Set the
scann.allow_blocked_operations creation
session-level parameter totrue
on the database:SET scann.allow_blocked_operations = true;
Assign the
SUPERUSER
privilege to the user that will run these queries on the database:CREATE USER USER_NAME WITH SUPERUSER PASSWORD PASSWORD;
Replace the following:
USER_NAME
: the name of the user you want to grant the privilege to.PASSWORD
: the password of the user.