HTTP Response Headers

When a query is executed using the HTTP end-point the response has a number of headers applied that can be used later.

HTTP/2 200 
date: Tue, 29 Jun 2021 09:32:06 GMT
content-type: application/json; charset=UTF-8
x-clickhouse-query-id: c4f6aba2-480f-4f67-9d5d-5662e44b45dc
x-clickhouse-format: JSON
x-clickhouse-timezone: UTC
x-hdx-query-stats: exec_time=4271 rows_read=0 bytes_read=0 num_partitions=4 num_peers=2

Header	Description	Example
`x-clickhouse-query-id`	Unique query identifier, supplied each time a query is executed.	`c4f6aba2-480f-4f67-9d5d-5662e44b45dc`
`x-clickhouse-format`	The format of the response Body.	`JSON`
`x-clickhouse-timezone`	The time zone applied to the data.	`UTC`
`x-hdx-query-stats`	Statistics and information covering how the query was executed and by how many resources	`exec_time=545 rows_read=48516556 bytes_read=194066224 num_partitions=18 num_peers=1`

x-hdx-query-stats

The Query stats supply the following information.

Query_stat	Description
`exec_time`	Execution time of the query in milliseconds
`catalog_resp_time_ms`	Execution time of catalog query in milliseconds
`num_partitions`	Number of HDX partitions accessed to answer the query
`memory_usage`	Memory used in bytes
`head_rows_read`	Count of rows handled by the query head
`head_bytes_read`	Number of uncompressed bytes parsed to answer the query
`num_peers`	Number of query-peers accessed to answer the query
`query_attempts`	Number of total times the query was tried, usually, 1
`peer_rows_read`	Count of rows read by all query peers
`peer_bytes_read`	Number of uncompressed bytes parsed by query peers
`result_rows`	Count of rows in the response set