The EXPLAIN ANALYZE statement executes a SQL query and generates a statement plan with execution statistics. The (DEBUG) option generates a URL to download a bundle with more details about the statement plan for advanced debugging. Statement plans provide information around SQL execution, which can be used to troubleshoot slow queries by figuring out where time is being spent, how long a processor (i.e., a component that takes streams of input rows and processes them according to a specification) is not doing work, etc. For more information about distributed SQL queries, see the DistSQL section of our SQL Layer Architecture docs.
The generated physical statement plan is encoded into a byte string after the fragment identifier (#) in the generated URL. The fragment is not sent to the web server; instead, the browser waits for the web server to return a decode.html resource, and then JavaScript on the web page decodes the fragment into a physical statement plan diagram. The statement plan is, therefore, not logged by a server external to the CockroachDB cluster and not exposed to the public internet.
Aliases
In CockroachDB, the following are aliases for EXPLAIN ANALYZE:
EXPLAIN ANALYSE
Synopsis
Parameters
| Parameter | Description |
|---|---|
PLAN |
New in v21.1: (Default) Executes the statement and returns CockroachDB's statement plan with planning and execution time for an explainable statement. For more information, see Default option. |
DISTSQL |
Return the statement plan and performance statistics as well as a generated link to a graphical distributed SQL physical statement plan tree. For more information, see DISTSQL option. |
DEBUG |
Generate a ZIP file containing files with detailed information about the query and the database objects referenced in the query. For more information, see DEBUG option. |
preparable_stmt |
The statement you want to execute and analyze. All preparable statements are explainable. |
Required privileges
The user requires the appropriate privileges for the statement being explained.
Success responses
Successful EXPLAIN ANALYZE statements return tables with the following details in the info column:
| Detail | Description |
|---|---|
| Global properties | The properties and statistics that apply to the entire statement plan. |
| Statement plan tree | A tree representation of the hierarchy of the statement plan. |
| Node details | The properties, columns, and ordering details for the current statement plan node in the tree. |
| Time | The time details for the statement. The total time is the planning and execution time of the statement. The execution time is the time it took for the final statement plan to complete. The network time is the amount of time it took to distribute the statement across the relevant nodes in the cluster. Some statements do not need to be distributed, so the network time is 0ms. |
If you use the DISTSQL option, the statement will also return a URL generated for a physical statement plan that provides high level information about how a statement will be executed. For details about reading the physical statement plan, see DistSQL Plan Viewer.
#) in the generated URL. The fragment is not sent to the web server; instead, the browser waits for the web server to return a decode.html resource, and then JavaScript on the web page decodes the fragment into a physical statement plan diagram. The statement plan is, therefore, not logged by a server external to the CockroachDB cluster and not exposed to the public internet.
If you use the DEBUG option, the statement will return a single text column with a URL and instructions to download the DEBUG bundle, which includes the physical statement plan.
Global properties
| Global property | Description |
|---|---|
| planning time | The total time the planner took to create a statement plan. |
| execution time | The time it took for the final statement plan to complete. |
| distribution | Shows whether the statement was distributed or local. If distribution is full, execution of the statement is performed by multiple nodes in parallel, then the results are returned by the gateway node. If local, the execution plan is performed only on the gateway node. Even if the execution plan is local, row data may be fetched from remote nodes, but the processing of the data is performed by the local node. |
| vectorized | Indicates whether the vectorized execution engine was used in this statement. |
| rows read from KV | The number of rows read from the Storage layer. |
| cumulative time spent in KV | The total amount of time spent in the Storage layer. |
| cumulative time spent due to contention | The total amount of time this statement was in contention with another transaction during execution. |
| maximum memory usage | The maximum amount of memory used by this statement anytime during its execution. |
| network usage | The amount of data transferred over the network while the statement was executed. If this value is 0 B, the statement was executed on a single node and didn't use the network. |
Statement plan tree properties
The statement plan tree shows
| Statement plan tree properties | Description |
|---|---|
| processor | Each processor in the statement plan hierarchy has a node with details about that phase of the statement. For example, a statement with a GROUP BY clause has a group processor with details about the cluster nodes, rows, and operations related to the GROUP BY operation. |
| nodes | The names of the CockroachDB cluster nodes affected by this phase of the statement. |
| regions | The regions where the affected nodes were located. |
| actual row count | The actual number of rows affected by this processor during execution. |
| estimated row count | The estimated number of rows affected by this processor according to the statement planner. |
| KV rows read | During scans, the number of rows in the Storage layer read by this phase of the statement. |
| KV bytes read | During scans, the amount of data read from the Storage layer during this phase of the statement. |
| table | The table and index used in a scan operation in a statement, in the form {table name}@{index name}. |
| spans | The interval of the key space read by the processor. If spans is FULL SCAN the table is scanned on all key ranges of the index. If spans is [/1 - /1] only the key with value 1 is read by the processor. |
Default option
New in v21.1:
By default, EXPLAIN ANALYZE uses the PLAN option. EXPLAIN ANALYZE and EXPLAIN ANALYZE (PLAN) produce the same output.
DISTSQL option
EXPLAIN ANALYZE (DISTSQL) generates a physical statement plan diagram in the DistSQL Plan Viewer. The DistSQL Plan Viewer displays the physical statement plan, as well as execution statistics. The statistics listed depend on the query type and the execution engine used. There will be multiple diagrams if the query contains subqueries or post-queries.
New in v21.1:
EXPLAIN ANALYZE (DISTSQL) can only be used as the top-level statement in a query.
DEBUG option
EXPLAIN ANALYZE (DEBUG) executes a query and generates a link to a ZIP file that contains the physical statement plan, execution statistics, statement tracing, and other information about the query.
| File | Description |
|---|---|
stats-<table>.sql |
Contains statistics for a table in the query. |
schema.sql |
Contains CREATE statements for objects in the query. |
env.sql |
Contains information about the CockroachDB environment. |
trace.txt |
Contains statement traces in plaintext format. |
trace.json |
Contains statement traces in JSON format. |
trace-jaeger.json |
Contains statement traces in JSON format that can be imported to Jaeger. |
distsql.html |
The query's physical statement plan. This diagram is identical to the one generated by EXPLAIN(DISTSQL). |
plan.txt |
The query execution plan. This is identical to the output of EXPLAIN (VERBOSE). |
opt.txt |
The statement plan tree generated by the cost-based optimizer. This is identical to the output of EXPLAIN (OPT). |
opt-v.txt |
The statement plan tree generated by the cost-based optimizer, with cost details. This is identical to the output of EXPLAIN (OPT, VERBOSE). |
opt-vv.txt |
The statement plan tree generated by the cost-based optimizer, with cost details and input column data types. This is identical to the output of EXPLAIN (OPT, TYPES). |
vec.txt |
The statement plan tree generated by the vectorized execution engine. This is identical to the output of EXPLAIN (VEC). |
vec-v.txt |
The statement plan tree generated by the vectorized execution engine. This is identical to the output of EXPLAIN (VEC, VERBOSE). |
statement.txt |
The SQL statement for the query. |
You can obtain this ZIP file by following the link provided in the EXPLAIN ANALYZE (DEBUG) output, or by activating statement diagnostics in the DB Console.
DistSQL plan viewer
The graphical diagram when using the DISTSQL option displays the processors and operations that make up the statement plan. While the text output from PLAN shows the statement plan across the cluster, DISTSQL shows details on each node involved in the query.
| Field | Description | Execution engine |
|---|---|---|
| <Processor>/<id> | The processor and processor ID used to read data into the SQL execution engine. A processor is a component that takes streams of input rows, processes them according to a specification, and outputs one stream of rows. For example, a "TableReader" processor reads in data, and an "Aggregator" aggregates input rows. |
Both |
| <table>@<index> | The index used by the processor. | Both |
| Spans | The interval of the key space read by the processor. For example, [/1 - /1] indicates that only the key with value 1 is read by the processor. |
Both |
| Out | The output columns. | Both |
| cluster nodes | The names of the CockroachDB cluster nodes involved in the execution of this processor. | Both |
| batches output | The number of batches of columnar data output. | Vectorized engine only |
| rows output | The number of rows output. | Vectorized engine only |
| IO time | How long the TableReader processor spent reading data from disk. | Vectorized engine only |
| stall time | How long the processor spent not doing work. This is aggregated into the stall time numbers as the query progresses down the tree (i.e., stall time is added up and overlaps with previous time). | Row-oriented engine only |
| bytes read | The size of the data read by the processor. | Both |
| rows read | The number of rows read by the processor. | Both |
| KV time | The total time this phase of the query was in the Storage layer. | Both |
| KV contention time | The time the Storage layer was in contention during this phase of the query. | Both |
| KV rows read | During scans, the number of rows in the Storage layer read by this phase of the query. | Both |
| KV bytes read | During scans, the amount of data read from the Storage layer during this phase of the query. | Both |
| @<n> | The index of the column relative to the input. | Both |
| max memory used | How much memory (if any) is used to buffer rows. | Row-oriented engine only |
| max disk used | How much disk (if any) is used to buffer data. Routers and processors will spill to disk buffering if there is not enough memory to buffer the data. | Row-oriented engine only |
| execution time | How long the engine spent executing the processor. | Vectorized engine only |
| max vectorized memory allocated | How much memory is allocated to the processor to buffer batches of columnar data. | Vectorized engine only |
| max vectorized disk used | How much disk (if any) is used to buffer columnar data. Processors will spill to disk buffering if there is not enough memory to buffer the data. | Vectorized engine only |
| left(@<n>)=right(@<n>) | The equality columns used in the join. | Both |
| stored side | The smaller table that was stored as an in-memory hash table. | Both |
| rows routed | How many rows were sent by routers, which can be used to understand network usage. | Row-oriented engine only |
| network latency | The latency time in nanoseconds between nodes in a stream. | Vectorized engine only |
| bytes sent | The number of actual bytes sent (i.e., encoding of the rows). This is only relevant when doing network communication. | Both |
| Render | The stage that renders the output. | Both |
| by hash | (Orange box) The router, which is a component that takes one stream of input rows and sends them to a node according to a routing algorithm. For example, a hash router hashes columns of a row and sends the results to the node that is aggregating the result rows. |
Both |
| unordered / ordered | (Blue box) A synchronizer that takes one or more output streams and merges them to be consumable by a processor. An ordered synchronizer is used to merge ordered streams and keeps the rows in sorted order. | Both |
| <data type> | If EXPLAIN (DISTSQL, TYPES) is specified, lists the data types of the input columns. |
Both |
| Response | The response back to the client. | Both |
Examples
To run the examples, initialize a demo cluster with the MovR workload.
Start the MovR database on a 3-node CockroachDB demo cluster with a larger data set.
cockroach demo movr --num-histories 250000 --num-promo-codes 250000 --num-rides 125000 --num-users 12500 --num-vehicles 3750 --nodes 3
EXPLAIN ANALYZE
Use EXPLAIN ANALYZE without an option, or equivalently with the PLAN option, to execute a query and display the physical statement plan with execution statistics.
For example, the following EXPLAIN ANALYZE statement executes a simple query against the MovR database and then displays the physical statement plan with execution statistics:
> EXPLAIN ANALYZE SELECT city, AVG(revenue) FROM rides GROUP BY city;
info
------------------------------------------------------------------------------------------
planning time: 527µs
execution time: 66ms
distribution: full
vectorized: true
rows read from KV: 125,000 (21 MiB)
cumulative time spent in KV: 142ms
maximum memory usage: 963 KiB
network usage: 2.5 KiB (24 messages)
regions: us-east1
• group
│ nodes: n1, n2, n3
│ regions: us-east1
│ actual row count: 9
│ estimated row count: 9
│ group by: city
│ ordered: +city
│
└── • scan
nodes: n1, n2, n3
regions: us-east1
actual row count: 125,000
KV rows read: 125,000
KV bytes read: 21 MiB
estimated row count: 125,000 (100% of the table; stats collected 11 minutes ago)
table: rides@primary
spans: FULL SCAN
(27 rows)
Time: 68ms total (execution 67ms / network 1ms)
EXPLAIN ANALYZE (DISTSQL)
Use EXPLAIN ANALYZE (DISTSQL) to execute a query, display the physical statement plan with execution statistics, and generate a link to a graphical DistSQL statement plan.
EXPLAIN ANALYZE (DISTSQL) SELECT city, AVG(revenue) FROM rides GROUP BY city;
info
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
planning time: 476µs
execution time: 107ms
distribution: full
vectorized: true
rows read from KV: 125,000 (21 MiB)
cumulative time spent in KV: 214ms
maximum memory usage: 963 KiB
network usage: 2.5 KiB (24 messages)
regions: us-east1
• group
│ nodes: n1, n2, n3
│ regions: us-east1
│ actual row count: 9
│ estimated row count: 9
│ group by: city
│ ordered: +city
│
└── • scan
nodes: n1, n2, n3
regions: us-east1
actual row count: 125,000
KV rows read: 125,000
KV bytes read: 21 MiB
estimated row count: 125,000 (100% of the table; stats collected 12 minutes ago)
table: rides@primary
spans: FULL SCAN
Diagram: https://cockroachdb.github.io/distsqlplan/decode.html#eJzEV11u4zYQfu8pCD5lUSUWqT9LT94stkWwib3IT4FFFQSMNHWE2KKXpBO5QW5SoKfoBXqUnqSQZG9sWaLlrJ19MUyOZjTzDb9vqCcsv45wgC8-nn78cImiRM0MxB6GBwIeIJ3CO_TL-eAMiSQGiX49H1x9RsdfisewgVMeQ5-NQeLgd0ywgSk2sIWvDTwRPAIpuchNT8WDJ3GGA9PASTqZqnz72sARF4CDJ6wSNQIc4Et2O4JzYDGIjokNHINiyagIX2TQm4hkzET-7osJS2WADjshZmOpQMRsHOJOiMMwi7wwzIh_FIYZc_LfP_xeGGamGYZZ11z8q_6Qp9zVDDFiaYwI4uoOBDbwYKoC1KNGj-QpffoNqWQMAfKdsSzXEU8VpCrh6dxk_vvP3CT4o0QCWBwgxzEc2y63b2cKFvv-EUVnyTE28C1T0R1IxKdqkr_TcbCBiwgvO0WM62cDl1tzHKViQ8ABeTbaY_1-OBQwZIqLjrUKdS9v5UDEICAOULF63_9y0x9c3vSvTk8PeuRd3oCrs4Mezf99GFz1L-f_IYNougSFV4BUrYysFVap6SXN2xm6Y_JuLcPr55e6aWPdL3F4WU81zs9lIA047veBc3F1dnOSw2Plq3NIYxC5n4F6tNOzaiDz7fL4bATNajwIVgtApmkdJLVo9Pkhn3T8VSCqadP6rO1q1n5j1vZK1qS9VNBWUtEJ8S2XiqeFTHT_-_uvMMygG4ZZ7B9vlgdzVJpxLjkpPKIZF_cLxSHR10GuHqBGJy1Cub0QNyuLQ7dTFuoZnuevK4t95DUoC-1WuzKP0U5ZNrRmiTzO_pTFaqcsVZJ8j7KQ3SpL962VxTFbKgtpqSy0PUdJW47uepof7or37a4FrrsdeW1iuJ63Tl7vyGwgr73WrnmMduTd0LOl82nvj7z2218L6G7J6701ebsNA5ZuAq3NtaCm1nOQE55KqFwP6iObOVoQD6FEV_KpiOCz4FHxmnI5KPyKjRikKq2kXJykpSlPcNmZVJ3JsjNdcSZFNqr2ckLMcqaOWYbGMOZihthoxCOm8nZZJvpUUC03y0jkCKM4kffLD5mojoz10rlNEX5jESmoRy7u0YgpSKNZgDzHK8_AwvLIEvWtwnIgxiBBJGyU_MmWL2f-quNcgCJIHgoAlkwLEfpm89yi8oV9DFKyIVTd2w3ibYBx2wPTdZzXAmNpgSE6YAjdCTA1J4ZqOWOtAlN1tvSEM_WMs7Xejt7ZeSVd1xrqu1ZjQ905Ceobqj_o2n5Sc1_91OOyhQL4HmnExXb2hMv-zrkel2YBaPj2_CHq7m7D1dee-Q0i5r26udTbW3M9LTBdvZJ0d6YkdvPM7Po6xlBHiyrVUcbZDap0HVU9MM1Ssvb5rKMM3SFlaua-voYt5r7vNVPGcnXN1Y99U9PbjUOC1qBiVlEx11HxdyYkmiOvFxLP1sLiaGBxnY3XRLvt18v180__BwAA__92ERda
(29 rows)
Time: 110ms total (execution 109ms / network 1ms)
To view the DistSQL Plan Viewer, point your browser to the URL provided.
EXPLAIN ANALYZE (DEBUG)
Use the DEBUG option to generate a ZIP file containing files with information about the query and the database objects referenced in the query. For example:
> EXPLAIN ANALYZE (DEBUG) SELECT city, AVG(revenue) FROM rides GROUP BY city;
info
--------------------------------------------------------------------------------
Statement diagnostics bundle generated. Download from the Admin UI (Advanced
Debug -> Statement Diagnostics History), via the direct link below, or using
the command line.
Admin UI: http://127.0.0.1:8080
Direct link: http://127.0.0.1:8080/_admin/v1/stmtbundle/645706706591449089
Command line: cockroach statement-diag list / download
(6 rows)
Time: 150ms total (execution 150ms / network 0ms)
Navigating to the URL will automatically download the ZIP file. You can also obtain the bundle by activating statement diagnostics in the DB Console.
See also
ALTER TABLEALTER SEQUENCEBACKUPCANCEL JOBCREATE DATABASEDROP DATABASEEXPLAINEXECUTEIMPORT- Indexes
INSERTPAUSE JOBRESETRESTORERESUME JOBSELECT- Selection Queries
SETSET CLUSTER SETTINGSHOW COLUMNSUPDATEUPSERT
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