This page describes newly identified limitations in the CockroachDB v20.2.19 release as well as unresolved limitations identified in earlier releases.
New limitations
Partitioning on ENUM values
Partitions cannot be created on columns of type ENUM.
Multiple arbiter indexes for INSERT ON CONFLICT DO UPDATE
CockroachDB does not currently support multiple arbiter indexes for INSERT ON CONFLICT DO UPDATE, and will return an error if there are multiple unique or exclusion constraints matching the ON CONFLICT DO UPDATE specification.
IMPORT into a table with partial indexes
CockroachDB does not currently support IMPORTs into tables with partial indexes.
To work around this limitation:
- Drop any partial indexes defined on the table.
- Perform the
IMPORT. - Recreate the partial indexes.
If you are performing an IMPORT of a PGDUMP with partial indexes:
- Drop the partial indexes on the PostgreSQL server.
- Recreate the
PGDUMP. IMPORTthePGDUMP.- Add partial indexes on the CockroachDB server.
Historical reads on restored objects
An object's historical data is not preserved upon RESTORE. This means that if an AS OF SYSTEM TIME query is issued on a restored object, the query will fail or the response will be incorrect because there is no historical data to query.
Spatial support limitations
CockroachDB supports efficiently storing and querying spatial data, with the following limitations:
Not all PostGIS spatial functions are supported.
The
AddGeometryColumnspatial function only allows constant arguments.The
AddGeometryColumnspatial function only allows thetruevalue for itsuse_typmodparameter.CockroachDB does not support the
@operator. Instead of using@in spatial expressions, we recommend using the inverse, with~. For example, instead ofa @ b, useb ~ a.CockroachDB does not yet support
INSERTs into thespatial_ref_systable. This limitation also blocks theogr2ogr -f PostgreSQLfile conversion command.CockroachDB does not yet support
DECLARE CURSOR, which prevents theogr2ogrconversion tool from exporting from CockroachDB to certain formats and prevents QGIS from working with CockroachDB. To work around this limitation, export data first to CSV or GeoJSON format.CockroachDB does not yet support storing spatial objects of more than two dimensions.
CockroachDB does not yet support Triangle or
TINspatial shapes.CockroachDB does not yet support Curve, MultiCurve, or CircularString spatial shapes.
CockroachDB does not yet support k-nearest neighbors.
CockroachDB does not support using schema name prefixes to refer to data types with type modifiers (e.g.,
public.geometry(linestring, 4326)). Instead, use fully-unqualified names to refer to data types with type modifiers (e.g.,geometry(linestring,4326)).Note that, in
IMPORT PGDUMPoutput,GEOMETRYandGEOGRAPHYdata type names are prefixed bypublic.. If the type has a type modifier, you must remove thepublic.from the type name in order for the statements to work in CockroachDB.
SET does not ROLLBACK in a transaction
SET does not properly apply ROLLBACK within a transaction. For example, in the following transaction, showing the TIME ZONE variable does not return 2 as expected after the rollback:
SET TIME ZONE +2;
BEGIN;
SET TIME ZONE +3;
ROLLBACK;
SHOW TIME ZONE;
timezone
------------
3
Unresolved limitations
Optimizer stale statistics deletion when columns are dropped
When a column is dropped from a multi-column index, the optimizer will not collect new statistics for the deleted column. However, the optimizer never deletes the old multi-column statistics. This can cause a buildup of statistics in
system.table_statisticsleading the optimizer to use stale statistics, which could result in sub-optimal plans. To workaround this issue and avoid these scenarios, explicitly delete those statistics from thesystem.table_statisticstable.Single-column statistics are not deleted when columns are dropped, which could cause minor performance issues.
Automatic statistics refresher may not refresh after upgrade
The automatic statistics refresher automatically checks whether it needs to refresh statistics for every table in the database upon startup of each node in the cluster. If statistics for a table have not been refreshed in a while, this will trigger collection of statistics for that table. If statistics have been refreshed recently, it will not force a refresh. As a result, the automatic statistics refresher does not necessarily perform a refresh of statistics after an upgrade. This could cause a problem, for example, if the upgrade moves from a version without histograms to a version with histograms. To refresh statistics manually, use CREATE STATISTICS.
Differences in syntax and behavior between CockroachDB and PostgreSQL
CockroachDB supports the PostgreSQL wire protocol and the majority of its syntax. However, CockroachDB does not support some of the PostgreSQL features or behaves differently from PostgreSQL because not all features can be easily implemented in a distributed system.
For a list of known differences in syntax and behavior between CockroachDB and PostgreSQL, see Features that differ from PostgreSQL.
Collation names that include upper-case or hyphens may cause errors
Using a collation name with upper-case letters or hyphens may result in errors.
For example, the following SQL will result in an error:
> CREATE TABLE nocase_strings (s STRING COLLATE "en-US-u-ks-level2");
> INSERT INTO nocase_strings VALUES ('Aaa' COLLATE "en-US-u-ks-level2"), ('Bbb' COLLATE "en-US-u-ks-level2");
> SELECT s FROM nocase_strings WHERE s = ('bbb' COLLATE "en-US-u-ks-level2");
ERROR: internal error: "$0" = 'bbb' COLLATE en_us_u_ks_level2: unsupported comparison operator: <collatedstring{en-US-u-ks-level2}> = <collatedstring{en_us_u_ks_level2}>
As a workaround, only use collation names that have lower-case letters and underscores.
Subqueries in SET statements
It is not currently possible to use a subquery in a SET or SET CLUSTER SETTING statement. For example:
> SET application_name = (SELECT 'a' || 'b');
ERROR: invalid value for parameter "application_name": "(SELECT 'a' || 'b')"
SQLSTATE: 22023
DETAIL: subqueries are not allowed in SET
Enterprise BACKUP does not capture database/table/column comments
The COMMENT ON statement associates comments to databases, tables, or columns. However, the internal table (system.comments) in which these comments are stored is not captured by a BACKUP of a table or database.
As a workaround, take a cluster backup instead, as the system.comments table is included in cluster backups.
Cold starts of large clusters may require manual intervention
If a cluster contains a large amount of data (>500GiB / node), and all nodes are stopped and then started at the same time, clusters can enter a state where they're unable to startup without manual intervention. In this state, logs fill up rapidly with messages like refusing gossip from node x; forwarding to node y, and data and metrics may become inaccessible.
To exit this state, you should:
- Stop all nodes.
- Set the following environment variables:
COCKROACH_SCAN_INTERVAL=60m, andCOCKROACH_SCAN_MIN_IDLE_TIME=1s. - Restart the cluster.
Once restarted, monitor the Replica Quiescence graph on the Replication Dashboard. When >90% of the replicas have become quiescent, conduct a rolling restart and remove the environment variables. Make sure that under-replicated ranges do not increase between restarts.
Requests to restarted node in need of snapshots may hang
When a node is offline, the Raft logs for the ranges on the node get truncated. When the node comes back online, it therefore often needs Raft snapshots to get many of its ranges back up-to-date. While in this state, requests to a range will hang until its snapshot has been applied, which can take a long time.
To work around this limitation, you can adjust the kv.snapshot_recovery.max_rate cluster setting to temporarily relax the throughput rate limiting applied to snapshots. For example, changing the rate limiting from the default 8 MB/s, at which 1 GB of snapshots takes at least 2 minutes, to 64 MB/s can result in an 8x speedup in snapshot transfers and, therefore, a much shorter interruption of requests to an impacted node:
> SET CLUSTER SETTING kv.snapshot_recovery.max_rate = '64mb';
Before increasing this value, however, verify that you will not end up saturating your network interfaces, and once the problem has resolved, be sure to reset to the original value.
Slow (or hung) backups and queries due to write intent buildup
Due to known bugs, transactions do not always clean up their write intents (newly written values) on commit or rollback. Garbage collection is also rather slow to react to them. This can cause the amount of unresolved write intents to build up over time. While this isn't necessarily a problem in itself, some operations do not handle large amounts of intents well. In particular, backups and queries that touch large numbers of values may become very slow and appear to hang.
To verify that intents may be causing an issue, open the Custom Chart debug page in the DB Console, and create a chart for the intentcount metric. This will show the number of intents present over time. The following query can also be used to get intent counts by range:
> SELECT * FROM (SELECT start_pretty, end_pretty, range_id, crdb_internal.range_stats(start_key)->'intent_count' AS intent_count FROM crdb_internal.ranges_no_leases) WHERE intent_count != '0';
To force cleanup of intents, either of the following methods can be used:
Do a high-priority scan of the table, which will resolve intents as it runs. Note that this may abort any conflicting transactions that are currently running. If the table has indexes, these can be cleaned by changing
<table>into<table>@<index>. Numeric table and/or index identifiers (e.g., as output by the intent query above) can be used instead of names by placing them in brackets:[<table-id>]or[<table-id>]@[<index-id>].> BEGIN PRIORITY HIGH; SELECT COUNT(*) FROM <table>; COMMIT;Manually enqueue the range for garbage collection. In the DB Console, open the Advanced Debug page, scroll down to Tracing and Profiling Endpoints, and click Run a range through an internal queue. Then select Queue: gc, enter the range ID as output by the intent query above, check SkipShouldQueue, and click Submit. The operation will succeed on the leaseholder node and error on the others; this is expected.
The progress and effect of the cleanup can be monitored via the intent count statistics described above.
Location-based time zone names
Certain features of CockroachDB require time zone data, for example, to support using location-based names as time zone identifiers. When starting a CockroachDB node on a machine missing time zone data, the node will not start.
To resolve this issue on Linux, install the tzdata library (sometimes called tz or zoneinfo).
To resolve this issue on Windows, download Go's official zoneinfo.zip and set the ZONEINFO environment variable to point to the zip file. For step-by-step guidance on setting environment variables on Windows, see this external article.
Make sure to do this across all nodes in the cluster and to keep this time zone data up-to-date.
Change data capture
Change data capture (CDC) provides efficient, distributed, row-level change feeds into Apache Kafka for downstream processing such as reporting, caching, or full-text indexing.
- Changefeeds only work on tables with a single column family (which is the default for new tables).
- Changefeeds do not share internal buffers, so each running changefeed will increase total memory usage. To watch multiple tables, we recommend creating a changefeed with a comma-separated list of tables.
- Many DDL queries (including
TRUNCATEandDROP TABLE) will cause errors on a changefeed watching the affected tables. You will need to start a new changefeed. - Changefeeds cannot be backed up or restored.
- Partial or intermittent sink unavailability may impact changefeed stability; however, ordering guarantees will still hold for as long as a changefeed remains active.
- Changefeeds cannot be altered. To alter, cancel the changefeed and create a new one with updated settings from where it left off.
- Additional target options will be added, including partitions and ranges of primary key rows.
- Changefeeds do not pick up data ingested with the
IMPORT INTOstatement. - Using a cloud storage sink only works with
JSONand emits newline-delimited json files.
DB Console may become inaccessible for secure clusters
Accessing the DB Console for a secure cluster now requires login information (i.e., username and password). This login information is stored in a system table that is replicated like other data in the cluster. If a majority of the nodes with the replicas of the system table data go down, users will be locked out of the DB Console.
AS OF SYSTEM TIME in SELECT statements
AS OF SYSTEM TIME can only be used in a top-level SELECT statement. That is, we do not support statements like INSERT INTO t SELECT * FROM t2 AS OF SYSTEM TIME <time> or two subselects in the same statement with differing AS OF SYSTEM TIME arguments.
Large index keys can impair performance
The use of tables with very large primary or secondary index keys (>32KB) can result in excessive memory usage. Specifically, if the primary or secondary index key is larger than 32KB the default indexing scheme for storage engine SSTables breaks down and causes the index to be excessively large. The index is pinned in memory by default for performance.
To work around this issue, we recommend limiting the size of primary and secondary keys to 4KB, which you must account for manually. Note that most columns are 8B (exceptions being STRING and JSON), which still allows for very complex key structures.
DB Console: Statements page latency reports
The Statements page does not correctly report "mean latency" or "latency by phase" for statements that result in schema changes or other background jobs.
Using LIKE...ESCAPE in WHERE and HAVING constraints
CockroachDB tries to optimize most comparisons operators in WHERE and HAVING clauses into constraints on SQL indexes by only accessing selected rows. This is done for LIKE clauses when a common prefix for all selected rows can be determined in the search pattern (e.g., ... LIKE 'Joe%'). However, this optimization is not yet available if the ESCAPE keyword is also used.
Using SQLAlchemy with CockroachDB
Users of the SQLAlchemy adapter provided by Cockroach Labs must upgrade the adapter to the latest release before upgrading to CockroachDB v20.2.
DB Console: CPU percentage calculation
For multi-core systems, the user CPU percent can be greater than 100%. Full utilization of one core is considered as 100% CPU usage. If you have n cores, then the user CPU percent can range from 0% (indicating an idle system) to (n*100)% (indicating full utilization).
DB Console: CPU count in containerized environments
When CockroachDB is run in a containerized environment (e.g., Kubernetes), the DB Console does not detect CPU limits applied to a container. Instead, the UI displays the actual number of CPUs provisioned on a VM.
TRUNCATE does not behave like DELETE
TRUNCATE is not a DML statement, but instead works as a DDL statement. Its limitations are the same as other DDL statements, which are outlined in Online Schema Changes: Limitations
Ordering tables by JSONB/JSON-typed columns
CockroachDB does not currently key-encode JSON values. As a result, tables cannot be ordered by JSONB/JSON-typed columns.
Current sequence value not checked when updating min/max value
Altering the minimum or maximum value of a series does not check the current value of a series. This means that it is possible to silently set the maximum to a value less than, or a minimum value greater than, the current value.
Using default_int_size session variable in batch of statements
When setting the default_int_size session variable in a batch of statements such as SET default_int_size='int4'; SELECT 1::IN, the default_int_size variable will not take affect until the next statement. This happens because statement parsing takes place asynchronously from statement execution.
As a workaround, set default_int_size via your database driver, or ensure that SET default_int_size is in its own statement.
COPY FROM statements are not supported in the CockroachDB SQL shell
The built-in SQL shell provided with CockroachDB (cockroach sql / cockroach demo) does not currently support importing data with the COPY statement.
To load data into CockroachDB, we recommend that you use an IMPORT. If you must use a COPY statement, you can issue the statement from the psql client command provided with PostgreSQL, or from another third-party client.
COPY syntax not supported by CockroachDB
CockroachDB does not yet support the following COPY syntax:
COPY ... TO. To copy data from a CockroachDB cluster to a file, use anEXPORTstatement.COPY ... FROM CSVCOPY ... FROM STDINwith a delimiter other than the default tab delimiter.COPY ... FROM ... WHERE <expr>
Import with a high amount of disk contention
IMPORT can sometimes fail with a "context canceled" error, or can restart itself many times without ever finishing. If this is happening, it is likely due to a high amount of disk contention. This can be mitigated by setting the kv.bulk_io_write.max_rate cluster setting to a value below your max disk write speed. For example, to set it to 10MB/s, execute:
> SET CLUSTER SETTING kv.bulk_io_write.max_rate = '10MB';
Placeholders in PARTITION BY
When defining a table partition, either during table creation or table alteration, it is not possible to use placeholders in the PARTITION BY clause.
Adding a column with sequence-based DEFAULT values
It is currently not possible to add a column to a table when the column uses a sequence as the DEFAULT value, for example:
> CREATE TABLE t (x INT);
> INSERT INTO t(x) VALUES (1), (2), (3);
> CREATE SEQUENCE s;
> ALTER TABLE t ADD COLUMN y INT DEFAULT nextval('s');
ERROR: nextval(): unimplemented: cannot evaluate scalar expressions containing sequence operations in this context
SQLSTATE: 0A000
Available capacity metric in the DB Console
If you are testing your deployment locally with multiple CockroachDB nodes running on a single machine (this is not recommended in production), you must explicitly set the store size per node in order to display the correct capacity. Otherwise, the machine's actual disk capacity will be counted as a separate store for each node, thus inflating the computed capacity.
Schema changes within transactions
Within a single transaction:
- DDL statements cannot be mixed with DML statements. As a workaround, you can split the statements into separate transactions. For more details, see examples of unsupported statements.
- As of version v2.1, you can run schema changes inside the same transaction as a
CREATE TABLEstatement. For more information, see this example. - A
CREATE TABLEstatement containingFOREIGN KEYorINTERLEAVEclauses cannot be followed by statements that reference the new table. - Database, schema, table, and user-defined type names cannot be reused. For example, you cannot drop a table named
aand then create (or rename) a different table with the namea. Similarly, you cannot rename a database namedatoband then create (or rename) a different database with the namea. As a workaround, splitRENAME TO,DROP, andCREATEstatements that reuse object names into separate transactions. - Schema change DDL statements inside a multi-statement transaction can fail while other statements succeed.
- As of v19.1, some schema changes can be used in combination in a single
ALTER TABLEstatement. For a list of commands that can be combined, seeALTER TABLE. For a demonstration, see Add and rename columns atomically. DROP COLUMNcan result in data loss if one of the other schema changes in the transaction fails or is canceled. To work around this, move theDROP COLUMNstatement to its own explicit transaction or run it in a single statement outside the existing transaction.
If a schema change within a transaction fails, manual intervention may be needed to determine which has failed. After determining which schema change(s) failed, you can then retry the schema changes.
Schema change DDL statements inside a multi-statement transaction can fail while other statements succeed
Schema change DDL statements that run inside a multi-statement transaction with non-DDL statements can fail at COMMIT time, even if other statements in the transaction succeed. This leaves such transactions in a "partially committed, partially aborted" state that may require manual intervention to determine whether the DDL statements succeeded.
If such a failure occurs, CockroachDB will emit a new CockroachDB-specific error code, XXA00, and the following error message:
transaction committed but schema change aborted with error: <description of error>
HINT: Some of the non-DDL statements may have committed successfully, but some of the DDL statement(s) failed.
Manual inspection may be required to determine the actual state of the database.
This limitation exists in versions of CockroachDB prior to 19.2. In these older versions, CockroachDB returned the Postgres error code 40003, "statement completion unknown".
If you must execute schema change DDL statements inside a multi-statement transaction, we strongly recommend checking for this error code and handling it appropriately every time you execute such transactions.
This error will occur in various scenarios, including but not limited to:
- Creating a unique index fails because values aren't unique.
- The evaluation of a computed value fails.
- Adding a constraint (or a column with a constraint) fails because the constraint is violated for the default/computed values in the column.
To see an example of this error, start by creating the following table.
CREATE TABLE T(x INT);
INSERT INTO T(x) VALUES (1), (2), (3);
Then, enter the following multi-statement transaction, which will trigger the error.
BEGIN;
ALTER TABLE t ADD CONSTRAINT unique_x UNIQUE(x);
INSERT INTO T(x) VALUES (3);
COMMIT;
pq: transaction committed but schema change aborted with error: (23505): duplicate key value (x)=(3) violates unique constraint "unique_x"
HINT: Some of the non-DDL statements may have committed successfully, but some of the DDL statement(s) failed.
Manual inspection may be required to determine the actual state of the database.
In this example, the INSERT statement committed, but the ALTER TABLE statement adding a UNIQUE constraint failed. We can verify this by looking at the data in table t and seeing that the additional non-unique value 3 was successfully inserted.
SELECT * FROM t;
x
+---+
1
2
3
3
(4 rows)
Schema changes between executions of prepared statements
When the schema of a table targeted by a prepared statement changes after the prepared statement is created, future executions of the prepared statement could result in an error. For example, adding a column to a table referenced in a prepared statement with a SELECT * clause will result in an error:
CREATE TABLE users (id INT PRIMARY KEY);
PREPARE prep1 AS SELECT * FROM users;
ALTER TABLE users ADD COLUMN name STRING;
INSERT INTO users VALUES (1, 'Max Roach');
EXECUTE prep1;
ERROR: cached plan must not change result type
SQLSTATE: 0A000
It's therefore recommended to explicitly list result columns instead of using SELECT * in prepared statements, when possible.
Size limits on statement input from SQL clients
CockroachDB imposes a hard limit of 16MiB on the data input for a single statement passed to CockroachDB from a client (including the SQL shell). We do not recommend attempting to execute statements from clients with large input.
Using \| to perform a large input in the SQL shell
In the built-in SQL shell, using the \| operator to perform a large number of inputs from a file can cause the server to close the connection. This is because \| sends the entire file as a single query to the server, which can exceed the upper bound on the size of a packet the server can accept from any client (16MB).
As a workaround, execute the file from the command line with cat data.sql | cockroach sql instead of from within the interactive shell.
New values generated by DEFAULT expressions during ALTER TABLE ADD COLUMN
When executing an ALTER TABLE ADD COLUMN statement with a DEFAULT expression, new values generated:
- use the default search path regardless of the search path configured in the current session via
SET SEARCH_PATH. - use the UTC time zone regardless of the time zone configured in the current session via
SET TIME ZONE. - have no default database regardless of the default database configured in the current session via
SET DATABASE, so you must specify the database of any tables they reference. - use the transaction timestamp for the
statement_timestamp()function regardless of the time at which theALTERstatement was issued.
Load-based lease rebalancing in uneven latency deployments
When nodes are started with the --locality flag, CockroachDB attempts to place the replica lease holder (the replica that client requests are forwarded to) on the node closest to the source of the request. This means as client requests move geographically, so too does the replica lease holder.
However, you might see increased latency caused by a consistently high rate of lease transfers between datacenters in the following case:
- Your cluster runs in datacenters which are very different distances away from each other.
- Each node was started with a single tier of
--locality, e.g.,--locality=datacenter=a. - Most client requests get sent to a single datacenter because that's where all your application traffic is.
To detect if this is happening, open the DB Console, select the Queues dashboard, hover over the Replication Queue graph, and check the Leases Transferred / second data point. If the value is consistently larger than 0, you should consider stopping and restarting each node with additional tiers of locality to improve request latency.
For example, let's say that latency is 10ms from nodes in datacenter A to nodes in datacenter B but is 100ms from nodes in datacenter A to nodes in datacenter C. To ensure A's and B's relative proximity is factored into lease holder rebalancing, you could restart the nodes in datacenter A and B with a common region, --locality=region=foo,datacenter=a and --locality=region=foo,datacenter=b, while restarting nodes in datacenter C with a different region, --locality=region=bar,datacenter=c.
Overload resolution for collated strings
Many string operations are not properly overloaded for collated strings, for example:
> SELECT 'string1' || 'string2';
?column?
------------------
string1string2
(1 row)
> SELECT ('string1' collate en) || ('string2' collate en);
pq: unsupported binary operator: <collatedstring{en}> || <collatedstring{en}>
Max size of a single column family
When creating or updating a row, if the combined size of all values in a single column family exceeds the max range size (512 MiB by default) for the table, the operation may fail, or cluster performance may suffer.
As a workaround, you can either manually split a table's columns into multiple column families, or you can create a table-specific zone configuration with an increased max range size.
Simultaneous client connections and running queries on a single node
When a node has both a high number of client connections and running queries, the node may crash due to memory exhaustion. This is due to CockroachDB not accurately limiting the number of clients and queries based on the amount of available RAM on the node.
To prevent memory exhaustion, monitor each node's memory usage and ensure there is some margin between maximum CockroachDB memory usage and available system RAM. For more details about memory usage in CockroachDB, see this blog post.
Privileges for DELETE and UPDATE
Every DELETE or UPDATE statement constructs a SELECT statement, even when no WHERE clause is involved. As a result, the user executing DELETE or UPDATE requires both the DELETE and SELECT or UPDATE and SELECT privileges on the table.
Correlated common table expressions
CockroachDB does not support correlated common table expressions. This means that a CTE cannot refer to a variable defined outside the scope of that CTE.
For example, the following query returns an error:
> SELECT * FROM users
WHERE id =
(WITH rides_home AS
(SELECT revenue FROM rides
WHERE end_address = address)
SELECT rider_id FROM rides_home);
ERROR: CTEs may not be correlated
SQLSTATE: 0A000
This query returns an error because the WITH rides_home clause references a column (address) returned by the SELECT statement at the top level of the query, outside the rides_home CTE definition.
ROLLBACK TO SAVEPOINT in high-priority transactions containing DDL
Transactions with priority HIGH that contain DDL and ROLLBACK TO SAVEPOINT are not supported, as they could result in a deadlock. For example:
> BEGIN PRIORITY HIGH; SAVEPOINT s; CREATE TABLE t(x INT); ROLLBACK TO SAVEPOINT s;
ERROR: unimplemented: cannot use ROLLBACK TO SAVEPOINT in a HIGH PRIORITY transaction containing DDL
SQLSTATE: 0A000
HINT: You have attempted to use a feature that is not yet implemented.
See: https://github.com/cockroachdb/cockroach/issues/46414
Concurrent SQL shells overwrite each other's history
The built-in SQL shell stores its command history in a single file by default (.cockroachsql_history). When running multiple instances of the SQL shell on the same machine. Therefore, each shell's command history can get overwritten in unexpected ways.
As a workaround, set the COCKROACH_SQL_CLI_HISTORY environment variable to different values for the two different shells, for example:
$ export COCKROACH_SQL_CLI_HISTORY=.cockroachsql_history_shell_1
$ export COCKROACH_SQL_CLI_HISTORY=.cockroachsql_history_shell_2
Passwords with special characters cannot be passed in connection parameter
CockroachDB does not allow passwords with special characters to be passed as a connection parameter to cockroach commands.
CockroachDB does not test for all connection failure scenarios
CockroachDB servers rely on the network to report when a TCP connection fails. In most scenarios when a connection fails, the network immediately reports a connection failure, resulting in a Connection refused error.
However, if there is no host at the target IP address, or if a firewall rule blocks traffic to the target address and port, a TCP handshake can linger while the client network stack waits for a TCP packet in response to network requests. To work around this kind of scenario, we recommend the following:
- When migrating a node to a new machine, keep the server listening at the previous IP address until the cluster has completed the migration.
- Configure any active network firewalls to allow node-to-node traffic.
- Verify that orchestration tools (e.g., Kubernetes) are configured to use the correct network connection information.
Some column-dropping schema changes do not roll back properly
Some schema changes that drop columns cannot be rolled back properly.
In some cases, the rollback will succeed, but the column data might be partially or totally missing, or stale due to the asynchronous nature of the schema change.
In other cases, the rollback will fail in such a way that will never be cleaned up properly, leaving the table descriptor in a state where no other schema changes can be run successfully.
To reduce the chance that a column drop will roll back incorrectly:
Perform column drops in transactions separate from other schema changes. This ensures that other schema change failures will not cause the column drop to be rolled back.
Drop all constraints (including unique indexes) on the column in a separate transaction, before dropping the column.
Drop any default values or computed expressions on a column before attempting to drop the column. This prevents conflicts between constraints and default/computed values during a column drop rollback.
If you think a rollback of a column-dropping schema change has occurred, check the jobs table. Schema changes with an error prefaced by cannot be reverted, manual cleanup may be required might require manual intervention.
Disk-spilling on joins with JSON columns
If the execution of a join query exceeds the limit set for memory-buffering operations (i.e., the value set for the sql.distsql.temp_storage.workmem cluster setting), CockroachDB will spill the intermediate results of computation to disk. If the join operation spills to disk, and at least one of the equality columns is of type JSON, CockroachDB returns the error unable to encode table key: *tree.DJSON. If the memory limit is not reached, then the query will be processed without error.
Disk-spilling not supported for unordered aggregation operations
Unordered aggregation operations do not support disk spilling, and are limited by the --max-sql-memory setting. If unordered aggregation operations exceed the amount of memory available to the SQL layer, CockroachDB will throw an error, and in some circumstances could crash.
Setting --max-sql-memory too high could result in performance problems due to increased memory consumption.
See the GitHub tracking issue for details.
GIN indexes cannot be partitioned
CockroachDB does not support partitioning GIN indexes, including spatial indexes.
GIN index scans can't be generated for some statement filters
CockroachDB cannot generate GIN index scans for statements with filters that have both JSON fetch values and containment operators. For example the following statement won't be index-accelerated:
SELECT * FROM mytable WHERE j->'a' @> '{"b": "c"}';
CockroachDB v20.1 and earlier would generate index scans for these filters, though it is not recommended as the normalization rules used to convert the filters into JSON containment expressions would sometimes produce inequivalent expressions.
The workaround is to rewrite the statement filters to avoid using both JSON fetch values and containment operators. The following statement is index-accelerated and equivalent to the non-accelerated statement above:
SELECT * FROM mytable WHERE j @> '{"a": {"b": "c"}}'
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