reader_permit: set_trace_state(): emit trace message linking to previous page

[denesb]

This method is called on the start of each page, updating the trace state stored on the permit to that of the current page. When doing so, emit a trace message, containing the session id of the previous page, so the per-page sessions can be stiched together later. Note that this message is only emitted if the cached read survived between the pages.

Example:

Tracing session: dcfc1570-ca3c-11ed-88d0-24443f03a8bb

 activity                                                                                                                              | timestamp                  | source    | source_elapsed | client
---------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------+----------------+-----------
														Execute CQL3 query | 2023-03-24 08:10:27.271000 | 127.0.0.1 |              0 | 127.0.0.1
												     Parsing a statement [shard 0] | 2023-03-24 08:10:27.271864 | 127.0.0.1 |             -- | 127.0.0.1
												  Processing a statement [shard 0] | 2023-03-24 08:10:27.271958 | 127.0.0.1 |             94 | 127.0.0.1
   Creating read executor for token 3274692326281147944 with all: {127.0.0.1} targets: {127.0.0.1} repair decision: NONE [shard 0] | 2023-03-24 08:10:27.271995 | 127.0.0.1 |            132 | 127.0.0.1
											     read_data: querying locally [shard 0] | 2023-03-24 08:10:27.271998 | 127.0.0.1 |            135 | 127.0.0.1
						     Start querying singular range {{3274692326281147944, pk{00026b73}}} [shard 0] | 2023-03-24 08:10:27.272003 | 127.0.0.1 |            140 | 127.0.0.1
								     [reader concurrency semaphore] admitted immediately [shard 0] | 2023-03-24 08:10:27.272006 | 127.0.0.1 |            143 | 127.0.0.1
									   [reader concurrency semaphore] executing read [shard 0] | 2023-03-24 08:10:27.272014 | 127.0.0.1 |            150 | 127.0.0.1
				 Querying cache for range {{3274692326281147944, pk{00026b73}}} and slice {(-inf, +inf)} [shard 0] | 2023-03-24 08:10:27.272022 | 127.0.0.1 |            159 | 127.0.0.1
 Page stats: 1 partition(s), 0 static row(s) (0 live, 0 dead), 3 clustering row(s) (3 live, 0 dead) and 0 range tombstone(s) [shard 0] | 2023-03-24 08:10:27.272076 | 127.0.0.1 |            212 | 127.0.0.1
							   Caching querier with key ab928e0d-b815-46b7-9a02-1fa2d9549477 [shard 0] | 2023-03-24 08:10:27.272084 | 127.0.0.1 |            221 | 127.0.0.1
													Querying is done [shard 0] | 2023-03-24 08:10:27.272087 | 127.0.0.1 |            224 | 127.0.0.1
										    Done processing - preparing a result [shard 0] | 2023-03-24 08:10:27.272106 | 127.0.0.1 |            242 | 127.0.0.1
														  Request complete | 2023-03-24 08:10:27.271259 | 127.0.0.1 |            259 | 127.0.0.1

Tracing session: dd3092f0-ca3c-11ed-88d0-24443f03a8bb

 activity                                                                                                                              | timestamp                  | source    | source_elapsed | client
---------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------+----------------+-----------
														Execute CQL3 query | 2023-03-24 08:10:27.615000 | 127.0.0.1 |              0 | 127.0.0.1
												     Parsing a statement [shard 0] | 2023-03-24 08:10:27.615223 | 127.0.0.1 |             -- | 127.0.0.1
												  Processing a statement [shard 0] | 2023-03-24 08:10:27.615310 | 127.0.0.1 |             87 | 127.0.0.1
   Creating read executor for token 3274692326281147944 with all: {127.0.0.1} targets: {127.0.0.1} repair decision: NONE [shard 0] | 2023-03-24 08:10:27.615346 | 127.0.0.1 |            124 | 127.0.0.1
											     read_data: querying locally [shard 0] | 2023-03-24 08:10:27.615349 | 127.0.0.1 |            126 | 127.0.0.1
						     Start querying singular range {{3274692326281147944, pk{00026b73}}} [shard 0] | 2023-03-24 08:10:27.615352 | 127.0.0.1 |            130 | 127.0.0.1
  Found cached querier for key ab928e0d-b815-46b7-9a02-1fa2d9549477 and range(s) {{{3274692326281147944, pk{00026b73}}}} [shard 0] | 2023-03-24 08:10:27.615358 | 127.0.0.1 |            135 | 127.0.0.1
													 Reusing querier [shard 0] | 2023-03-24 08:10:27.615362 | 127.0.0.1 |            139 | 127.0.0.1
			   Continuing paged query, previous page's trace session is dcfc1570-ca3c-11ed-88d0-24443f03a8bb [shard 0] | 2023-03-24 08:10:27.615364 | 127.0.0.1 |            141 | 127.0.0.1
									   [reader concurrency semaphore] executing read [shard 0] | 2023-03-24 08:10:27.615371 | 127.0.0.1 |            148 | 127.0.0.1
 Page stats: 1 partition(s), 0 static row(s) (0 live, 0 dead), 1 clustering row(s) (1 live, 0 dead) and 0 range tombstone(s) [shard 0] | 2023-03-24 08:10:27.615385 | 127.0.0.1 |            163 | 127.0.0.1
													Querying is done [shard 0] | 2023-03-24 08:10:27.615583 | 127.0.0.1 |            360 | 127.0.0.1
										    Done processing - preparing a result [shard 0] | 2023-03-24 08:10:27.615730 | 127.0.0.1 |            507 | 127.0.0.1
														  Request complete | 2023-03-24 08:10:27.615518 | 127.0.0.1 |            518 | 127.0.0.1

See the message:

Continuing paged query, previous page's trace session is dcfc1570-ca3c-11ed-88d0-24443f03a8bb [shard 0] | 2023-03-24 08:10:27.615364 | 127.0.0.1 |            141 | 127.0.0.1

This is a folow-up to #13255
Refs: #12781

[denesb]

To have a reliably printed trace message we have to store the trace session id in the paging state, then we could move this message to the pager (coordinator). As-is this message will be printed on each replica (that has a cached read).

[scylladb-promoter]

CI state SUCCESS - https://jenkins.scylladb.com/job/scylla-master/job/scylla-ci/287/