nickva commented on code in PR #5602:
URL: https://github.com/apache/couchdb/pull/5602#discussion_r2316517635
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src/couch_srt/README.md:
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+# couch_srt: Couch Stats Resource Tracker aka CSRT
+
+The `couch_srt` app introduces the Couch Stats Resource Tracker, aka CSRT for
+short. CSRT is a real time stats tracking system that tracks the quantity of
+resources induced at the process level in a live queryable manner, while also
+generating process lifetime reports containing statistics on the total resource
+load of a request, as a function of CouchDB operations like dbs/docs opened,
+view and changes rows read, changes returned vs processed, Javascript filter
+usage, request duration, and more. This system is a paradigm shift in CouchDB
+visibility and introspection, allowing for expressive real time querying
+capabilities to introspect, understand, and aggregate CouchDB internal resource
+usage, as well as powerful filtering facilities for conditionally generating
+reports on "heavy usage" requests or "long/slow" requests. CSRT also extends
+`recon:proc_window` with `couch_srt:proc_window` allowing for the same style of
+battle hardened introspection with Recon's excellent `proc_window`, but with
the
+sample window over any of the CSRT tracked CouchDB stats!
+
+CSRT does this by piggy-backing off of the existing metrics tracked by way of
+`couch_stats:increment_counter` at the time when the local process induces
those
+metrics inc calls, and then CSRT updates an ets entry containing the context
+information for the local process, such that global aggregate queries can be
+performed against the ets table as well as the generation of the process
+resource usage reports at the conclusions of the process's lifecyle.The ability
+to do aggregate querying in realtime in addition to the process lifecycle
+reports for post facto analysis over time, is a cornerstone of CSRT that is the
+result of a series of iterations until a robust and scalable aproach was built.
+
+The real time querying is achieved by way of a global ets table with
+`read_concurrency`, `write_concurrency`, and `decentralized_counters` enabled.
+Great care was taken to ensure that _zero_ concurrent writes to the same key
+occure in this model, and this entire system is predicated on the fact that
+incremental updates to `ets:update_counters` provides *really* fast and
+efficient updates in an atomic and isolated fashion when coupled with
+decentralized counters and write concurrency. Each process that calls
+`couch_stats:increment_counter` tracks their local context in CSRT as well,
with
+zero concurrent writes from any other processes. Outside of the context setup
+and teardown logic, _only_ operations to `ets:update_counter` are performed,
one
+per process invocation of `couch_stats:increment_counter`, and one for
+coordinators to update worker deltas in a single batch, resulting in a 1:1
ratio
+of ets calls to real time stats updates for the primary workloads.
+
+The primary achievement of CSRT is the core framework iself for concurrent
+process local stats tracking and real time RPC delta accumulation in a scalable
+manner that allows for real time aggregate querying and process lifecycle
+reports. This took several versions to find a scalable and robust approach that
+induced minimal impact on maximum system throughput. Now that the framework is
+in place, it can be extended to track any further desired process local uses of
+`couch_stats:increment_counter`. That said, the currently selected set of stats
+to track was heavily influenced by the challenges in reotractively
understanding
+the quantity of resources induced by a query like `/db/_changes?since=$SEQ`, or
+similarly, `/db/_find`.
+
+CSRT started as an extension of the Mango execution stats logic to `_changes`
+feeds to get proper visibility into quantity of docs read and filtered per
+changes request, but then the focus inverted with the realization that we
should
+instead use the existing stats tracking mechanisms that have already been
deemed
+critical information to track, which then also allows for the real time
tracking
+and aggregate query capabilities. The Mango execution stats can be ported into
+CSRT itself and just become one subset of the stats tracked as a whole, and
+similarly, any additional desired stats tracking can be easily added and will
+be picked up in the RPC deltas and process lifetime reports.
+
+## A Simple Example
+
+Given a databse `foo` with 11k documents containg a `doc.value` field that is
an
+integer value which can be filtered in a design doc by way of even and odd. If
+we instantiate a series of while loops in parallel making requests of the form:
+
+> GET /foo/_changes?filter=bar/even&include_docs=true
+
+We can generate a good chunk of load on a local laptop dev setup, resulting in
+requests that take a few seconds to load through the changes feed, fetch all
11k
+docs, and then funnel them through the Javascript engine to filter for even
+valued docs; this allows us time to query these heavier requests live and see
+them in progress with the real time stats tracking and querying capabilities of
+CSRT.
+
+For example, let's use `couch_srt:proc_window/3` as one would do with
+`recon:proc_window/3` to get an idea of the heavy active processes on the
+system:
+
+```
+(node1@127.0.0.1)2> rp([{PR, couch_srt:to_json(couch_srt:get_resource(PR))} ||
{PR, _, _} <- couch_srt:proc_window(ioq_calls, 3, 1000)]).
+[{{<0.5090.0>,#Ref<0.2277656623.605290499.37969>},
+ #{changes_returned => 3962,db_open => 10,dbname => <<"foo">>,
+ docs_read => 7917,docs_written => 0,get_kp_node => 54,
+ get_kv_node => 1241,ioq_calls => 15834,js_filter => 7917,
+ js_filtered_docs => 7917,nonce => <<"cc5a814ceb">>,
+ pid_ref =>
+ <<"<0.5090.0>:#Ref<0.2277656623.605290499.37969>">>,
+ rows_read => 7917,
+ started_at => <<"2025-07-21T17:25:08.784z">>,
+ type =>
+ <<"coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes">>,
+ updated_at => <<"2025-07-21T17:25:13.051z">>,
+ username => <<"adm">>}},
+ {{<0.5087.0>,#Ref<0.2277656623.606601217.92191>},
+ #{changes_returned => 4310,db_open => 10,dbname => <<"foo">>,
+ docs_read => 8624,docs_written => 0,get_kp_node => 58,
+ get_kv_node => 1358,ioq_calls => 17248,js_filter => 8624,
+ js_filtered_docs => 8624,nonce => <<"0e625c723a">>,
+ pid_ref =>
+ <<"<0.5087.0>:#Ref<0.2277656623.606601217.92191>">>,
+ rows_read => 8624,
+ started_at => <<"2025-07-21T17:25:08.424z">>,
+ type =>
+ <<"coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes">>,
+ updated_at => <<"2025-07-21T17:25:13.051z">>,
+ username => <<"adm">>}},
+ {{<0.5086.0>,#Ref<0.2277656623.605290499.27728>},
+ #{changes_returned => 4285,db_open => 10,dbname => <<"foo">>,
+ docs_read => 8569,docs_written => 0,get_kp_node => 57,
+ get_kv_node => 1349,ioq_calls => 17138,js_filter => 8569,
+ js_filtered_docs => 8569,nonce => <<"962cda1645">>,
+ pid_ref =>
+ <<"<0.5086.0>:#Ref<0.2277656623.605290499.27728>">>,
+ rows_read => 8569,
+ started_at => <<"2025-07-21T17:25:08.406z">>,
+ type =>
+ <<"coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes">>,
+ updated_at => <<"2025-07-21T17:25:13.051z">>,
+ username => <<"adm">>}}]
+ok
+```
+
+This shows us the top 3 most active processes (being tracked in CSRT) over the
+next 1000 milliseconds, sorted by number of `ioq_calls` induced! All of three
+of these processes are incurring heavy usage, reading many thousands of docs
+with 15k+ IOQ calls and heavy JS filter usage, exactly the types of requests
+you want to be alerted to. CSRT's proc window logic is built on top of Recon's,
+which doesn't return the process info itself, so you'll need to fetch the
+process status with `couch_srt:get_resource/1` and then pretty print it with
+`couch_srt:to_json/1`.
+
+The output above is a real time snapshot of the live running system and shows
+processes actively inducing additional resource usage, so these CSRT context
+values are just a time snapshot of where that process was at, as of the
+`updated_at` timestamp. We can reference the nonce value to search through the
+report logs for a final report, assuming the given context ended up using
+sufficient resources to trigger a logger matcher lifetime report. The above
+changes requests were induced specifically to induce reports as well, so
+unsurprisingly we have reports for all three.
+
+However, I want to first show the existing visibility into these changes
+requests exposed by the raw HTTP logs to highlight the impact of the CSRT
+reports and new visibility into request workloads exposed.
+
+First, let's look at the existing HTTP logs for those 3 requests:
+
+```
+(chewbranca)-(jobs:1)-(~/src/couchdb_csrt_v3)
+(! 9872)-> grep 'cc5a814ceb\|0e625c723a\|962cda1645' ./dev/logs/node1.log |
grep -v '^\[report]'
+[notice] 2025-07-21T17:25:14.520641Z node1@127.0.0.1 <0.5087.0> 0e625c723a
localhost:15984 127.0.0.1 adm GET
/foo/_changes?filter=bar/even&asdf=fdsa&include_docs=true 200 ok 6096
+[notice] 2025-07-21T17:25:14.521417Z node1@127.0.0.1 <0.5086.0> 962cda1645
localhost:15984 127.0.0.1 adm GET
/foo/_changes?filter=bar/even&asdf=fdsa&include_docs=true 200 ok 6115
+[notice] 2025-07-21T17:25:14.844317Z node1@127.0.0.1 <0.5090.0> cc5a814ceb
localhost:15984 127.0.0.1 adm GET
/foo/_changes?filter=bar/even&asdf=fdsa&include_docs=true 200 ok 6059
+```
+
+So we see the requests were made, and we can see it's doing `include_docs=true`
+as well as using a customer filter, both obvious indications that this is a
+potentially heavier request, however, we don't know if database foo had a
+thousand docs or a billion docs, whether those docs were small or large, nor
any
+indication of the computational complexity of the reference filter function.
+This makes it challenging to retroactively correlate heavy resource usage at a
+hardware level with the underlying requests that induced those workloads,
+especially if the heavy requests are an inconspicuous subset of the full
+database workload.
+
+CSRT resolves this by providing a real time querying system to find the active
+heavy proceses, live, as well as a process lifecyle reporting engine providing
+detailed analysis of the workloads induced by the request.
+
+Let's assume we had the default IOQ logger matcher enabled, with the default
+configuration of logging any requests inducing more than 10k IOQ calls, which
+would catch all three of our requests above, even though they're all still
+going. As a result, we generate process lifecylce reports for all three of
those
+requests, as we can see:
+
+```
+(chewbranca)-(jobs:1)-(~/src/couchdb_csrt_v3)
+(! 9873)-> grep 'cc5a814ceb\|0e625c723a\|962cda1645' ./dev/logs/node1.log |
grep '^\[report]'
+[report] 2025-07-21T17:25:14.520787Z node1@127.0.0.1 <0.5174.0> --------
[csrt-pid-usage-lifetime changes_returned=5500 db_open=10 dbname="foo"
docs_read=11001 get_kp_node=72 get_kv_node=1754 ioq_calls=22002 js_filter=11001
js_filtered_docs=11001 nonce="0e625c723a"
pid_ref="<0.5087.0>:#Ref<0.2277656623.606601217.92191>" rows_read=11001
started_at="2025-07-21T17:25:08.424z"
type="coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes"
updated_at="2025-07-21T17:25:14.520z" username="adm"]
+[report] 2025-07-21T17:25:14.521578Z node1@127.0.0.1 <0.5155.0> --------
[csrt-pid-usage-lifetime changes_returned=5500 db_open=10 dbname="foo"
docs_read=11001 get_kp_node=72 get_kv_node=1754 ioq_calls=22002 js_filter=11001
js_filtered_docs=11001 nonce="962cda1645"
pid_ref="<0.5086.0>:#Ref<0.2277656623.605290499.27728>" rows_read=11001
started_at="2025-07-21T17:25:08.406z"
type="coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes"
updated_at="2025-07-21T17:25:14.521z" username="adm"]
+[report] 2025-07-21T17:25:14.844436Z node1@127.0.0.1 <0.5213.0> --------
[csrt-pid-usage-lifetime changes_returned=5500 db_open=10 dbname="foo"
docs_read=11001 get_kp_node=72 get_kv_node=1754 ioq_calls=22002 js_filter=11001
js_filtered_docs=11001 nonce="cc5a814ceb"
pid_ref="<0.5090.0>:#Ref<0.2277656623.605290499.37969>" rows_read=11001
started_at="2025-07-21T17:25:08.784z"
type="coordinator-{chttpd_db:handle_changes_req}:GET:/foo/_changes"
updated_at="2025-07-21T17:25:14.844z" username="adm"]
+```
+
+We find the process lifecycle reports for the requests with the three grep'ed
on
+nonces, and we can see they all read the 11k core documents, plus the one
design
+document, JS filtered all 11,001 docs, and then only returned the 5500 doc's
+containing an even `doc.value` field.
+
+This also shows the discrepancy between the quantity of induced resource usage
+to actually generate a request, relative to the magnitude of the data returned.
+All of our `doc.value` fields were positive integers, if we had a filter
+function searching for negative `doc.value` results, we would have found none,
+resulting in `changes_returned=0`, but we would have still induced the 11,001
+doc loads and Javascript filter calls.
+
+CSRT is specifically built to automatically find and report these types of
+workload discrepancies and in general to help highlight where individual HTTP
+requests use drastically more resources than the median workloads.
+
+See the dedicated proc window documentation section further down for more info.
+
+## Additional Overview and Examples
+
+The query and HTTP API's are well documented and tested (h/t @iilyak) and
+provide an excellent overview of the interaction patterns and query
capabilities
+of CSRT. Those can be found at:
+
+* `couch_srt_query.erl` "Query API functions"
+ -
https://github.com/apache/couchdb/blob/93bc894380056ccca1f77415454e991c4d914249/src/couch_stats/src/couch_srt_query.erl#L319-L674
+ - the above highlighted functions are well tested, typespec'ed, and have
+ auxilary documentation and examples, an excellent resource
+* the `couch_srt_query_tests.erl` Eunit tests are an excellent overview of
utilizing
+ the `couch_srt_query:` API from Erlang to find, filter, and aggregate CSRT
real
+ time contexts
+ -
https://github.com/apache/couchdb/blob/93bc894380056ccca1f77415454e991c4d914249/src/couch_stats/test/eunit/couch_srt_query_tests.erl
+* similarly, the `couch_srt_httpd_tests.erl` Eunit tests are an excellent
overview of
+ performing the same style `couch_srt_query:` queries, but through the HTTP
API
+ -
https://github.com/apache/couchdb/blob/93bc894380056ccca1f77415454e991c4d914249/src/couch_stats/test/eunit/couch_srt_httpd_tests.erl
+* Additionally there's the `couch_srt_logger_tests.erl` Eunit tests which
demonstrate
+ the different default logger matchers in action
+ -
https://github.com/apache/couchdb/blob/93bc894380056ccca1f77415454e991c4d914249/src/couch_stats/test/eunit/couch_srt_logger_tests.erl
+
+# CSRT Config Keys
+
+## -define(CSRT, "csrt").
+
+> config:get("csrt").
+
+Primary CSRT config namespace: contains core settings for enabling different
+layers of functionality in CSRT, along with global config settings for limiting
+data volume generation.
+
+## -define(CSRT_MATCHERS_ENABLED, "csrt_logger.matchers_enabled").
+
+> config:get("csrt_logger.matchers_enabled").
+
+Config toggles for enabling specific builtin logger matchers, see the dedicated
+section below on `# CSRT Default Matchers`.
+
+## -define(CSRT_MATCHERS_THRESHOLD, "csrt_logger.matchers_threshold").
+
+> config:get("csrt_logger.matchers_threshold").
+
+Config settings for defining the primary `Threshold` value of the builtin
logger
+matchers, see the dedicated section below on `# CSRT Default Matchers`.
+
+## -define(CSRT_MATCHERS_DBNAMES, "csrt_logger.dbnames_io").
+
+> config:get("csrt_logger.matchers_enabled").
+
+Config section for setting `$db_name = $threshold` resulting in instantiating a
+"dbnames_io" logger matcher for each `$db_name` that will generate a CSRT
+lifecycle report for any contexts that that induced more operations on _any_
one
+field of `ioq_calls|get_kv_node|get_kp_node|docs_read|rows_read` that is
greater
+than `$threshold` and is on database `$db_name`.
+
+This is basically a simple matcher for finding heavy IO requests on a
particular
+database, in a manner amenable to key/value pair specifications in this .ini
+file until a more sophisticated declarative model exists. In particular, it's
+not easy to sequentially generate matchspecs by way `ets:fun2ms/1`, and so an
+alternative mechanism for either dynamically assembling an `#rctx{}` to match
+against or generating the raw matchspecs themselves is warranted.
+
+# CSRT Code Markers
+
+## -define(CSRT_ETS, csrt_server).
+
+This is the reference to the CSRT ets table, it's managed by `csrt_server` so
+that's where the name originates from.
+
+## -define(MATCHERS_KEY, {csrt_logger, all_csrt_matchers}).
+
+This marker is where the active matchers are written to in `persisten_term` for
+concurrently and parallelly and accessing the logger matchers in the CSRT
+tracker processes for lifecycle reporting.
+
+# CSRT Process Dictionary Markers
+
+## -define(PID_REF, {csrt, pid_ref}).
+
+This marker is for the core storing the core `PidRef` identifier. The key idea
+here is that a lifecycle is a context lifecycle is contained to within the
given
+`PidRef`, meaning that a `Pid` can instantiate different CSRT lifecycles and
+pass those to different workers.
+
+This is specifically necessary for long running processes that need to handle
+many CSRT context lifecycles over the course of that individual process's
+lifecycle independent. In practice, this is immediately needed for the actual
+coordinator lifecycle tracking, as `chttpd` uses a worker pool of http request
+handlers that can be re-used, so we need a way to create a CSRT lifecycle
+corresponding to the given request currently being serviced. This is also
+intended to be used in other long running processes, like IOQ or `couch_js`
pids
+such that we can track the specific context inducing the operations on the
+`couch_file` pid or indexer or replicator or whatever.
+
+Worker processes have a more clear cut lifecycle, but either style of process
+can be exit'ed in a manner that skips the ability to do cleanup operations, so
+additionally there's a dedicated tracker process spawned to monitor the process
+that induced the CSRT context such that we can do the dynamic logger matching
+directly in these tracker processes and also we can properly cleanup the ets
+entries even if the Pid crashes.
+
+## -define(TRACKER_PID, {csrt, tracker}).
+
+A handle to the spawned tracker process that does cleanup and logger matching
+reports at the end of the process lifecycle. We store a reference to the
tracker
+pid so that for explicit context destruction, like in `chttpd` workers after a
+request has been serviced, we can update stop the tracker and perform the
+expected cleanup directly.
+
+## -define(DELTA_TA, {csrt, delta_ta}).
+
+This stores our last delta snapshot to track progress since the last
incremental
+streaming of stats back to the coordinator process. This will be updated after
+the next delta is made with the latest value. Eg this stores `T0` so we can do
+`T1 = get_resource()` `make_delta(T0, T1)` and then we save `T1` as the new
`T0`
+for use in our next delta.
+
+## -define(LAST_UPDATED, {csrt, last_updated}).
+
+This stores the integer corresponding to the `erlang:monotonic_time()` value of
+the most recent `updated_at` value. Basically this lets us utilize a pdict
+value to be able to turn `update_at` tracking into an incremental operation
that
+can be chained in the existing atomic `ets:update_counter` and
+`ets:update_element` calls.
+
+The issue being that our updates are of the form `+2 to ioq_calls for
$pid_ref`,
+which ets does atomically in a guaranteed `atomic` and `isolated` manner. The
+strict use of the atomic operations for tracking these values is why this
+system works effeciently at scale. This means that we can increment counters on
+all of the stats counter fields in a batch, very quickly, but for tracking
+`updated_at` timestamps we'd need to either do an extra ets call to get the
last
+`updated_at` value, or do an extra ets call to `ets:update_element` to set the
+`updated_at` value to `couch_srt_util:tnow()`. The core problem with this is
that the
+batch inc operation is essentially the only write operation performed after the
+initial context setting of dbname/handler/etc; this means that we'd literally
+double the number of ets calls induced to track CSRT updates, just for tracking
+the `updated_at`. So instead, we rely on the fact that the local process
+corresponding to `$pid_ref` is the _only_ process doing updates so we know the
+last `updated_at` value will be the last time this process updated the data. So
+we track that value in the pdict and then take a delta between `tnow()` and
+`updated_at`, and then `updated_at` becomes a value we can sneak into the other
+integer counter updates we're already performing!
+
+# Primary Config Toggles
+
+# CSRT (?CSRT="csrt") Config Settings
+
+## config:get(?CSRT, "enable", false).
+
+Core enablement toggle for CSRT, defaults to false. Enabling this setting
+intiates local CSRT stats collection as well as shipping deltas in RPC
+responses to accumulate in the coordinator.
+
+This does _not_ trigger the new RPC spawn metrics, and it does not enable
+reporting for any of the rctx types.
+
+*NOTE*: you *MUST* have all nodes in the cluster running a CSRT aware CouchDB
+_before_ you enable it on any node, otherwise the old version nodes won't know
+how to handle the new RPC formats including an embedded Delta payload.
+
+## config:get(?CSRT, "enable_init_p", false).
+
+Enablement of tracking new metric counters for different `fabric_rpc`
operations
+spawned by way of `rexi_server:init_p/3`. This is the primary mechanism for
+inducing database RPC operations within CouchDB, and these init_p metrics aim
to
+provide node lever understandings of the workloads being induced by other
+coordinator proceses. This is especially relevant for databases on subsets of a
+cluster resulting in non-uniform workloads, these metrics are tailored to
+provide insight into what work is being spawned on each node in the cluster as
a
+function of time.
+
+## config:get(?CSRT, "enable_reporting", false).
+
+This is the primary toggle for enabling CSRT process lifetime reports
containing
+detailed information about the quantity of work induced by the given
+request/worker/etc. This is the top level toggle for enabling _any_ reporting,
+and there also exists `config:get(?CSRT, "enable_rpc_reporting", false).` to
+disable the reporting of any individual RPC workers, leaving the coordinator
+responsible of generating a report with the accumulated deltas.
+
+## config:get(?CSRT, "enable_rpc_reporting", false).
+
+This enables the possibility of RPC workers generating reports. They still need
+to hit the configured thresholds to induce a report, but this will generate
CSRT
+process lifetime reports for individual RPC workers that trigger the configured
+logger thresholds. This allows for quantifying per node resource usage when
+desired, as otherwise the reports are at the http request level and don't
+provide per node stats.
+
+The key idea here is that having RPC level CSRT process lifetime reporting is
+incredibly useful, but can also generate large quantities of data. For example,
+a view query on a Q=64 database will stream results from 64 shard replicas,
+resulting in at least 64 RPC reports, plus any that might have been generated
+from RPC workers that "lost" the race for shard replica. This is very useful,
+but a lot of data given the verbose nature of funneling it through the RSyslog
+reports, however, the ability to write directly to something like ClickHouse or
+another columnar store would be great.
+
+Until there's an efficient storage mechanism to stream the results to, the
+rsyslog entries work great and are very practical, but care must be taken to
+not generate too much data for aggregate queries as they generate at least `Qx`
+more report than an individual report per http request from the coordinator.
+This setting exists as a way to either a) utilize the logger matcher configured
+thresholds to allow for _any_ rctx's to be recorded when they induce heavy
+operations, either Coordinator or RPC worker; or b) to _only_ log workloads at
+the coordinator level.
+
+NOTE: this setting exists because we lack an expressive enough config
+declaration to easily chain the matchspec constructions as `ets:fun2ms/1` is a
+special compile time parse transform macro that requires the fully definition
to
+be specified directly, it cannot be iteractively constructed. That said, you
+_can_ register matchers through remsh with more specific and fine grained
+pattern matching, and a more expressive system for defining matchers are being
+explored.
+
+## config:get_boolean(?CSRT, "should_truncate_reports", true)
+
+Enables truncation of the CSRT process lifetime reports to not include any
+fields that are zero at the end of process lifetime, eg don't include
+`js_filter=0` in the report if the request did not induce Javascript filtering.
+
+This can be disabled if you really care about consistent fields in the report
+logs, but this is a log space saving mechanism, similar to disabling RPC
+reporting by default, as its a simple way to reduce overall volume
+
+## config:get(?CSRT, "randomize_testing", true).
+
+This is a `make eunit` only feature toggle that will induce randomness into the
+cluster's `couch_srt:is_enabled()` state, specifically to utilize the test
suite to
+exercise edge case scenarios and failures when CSRT is only conditionally
+enabled, ensuring that it gracefuly and robustly handles errors without fallout
+to the underlying http clients.
+
+The idea here is to introduce randomness into whether CSRT is enabled across
all
+the nodes to simulate clusters with heterogeneous CSRT enablement and also to
+ensure that CSRT works properly when toggled on/off wihout causing any
+unexpected fallout to the client requests.
+
+This is a config toggle specifically so that the actual CSRT tests can disable
+it for making accurate assertions about resource usage traacking, and is not
+intended to be used directly.
+
+## config:get_integer(?CSRT, "query_limit", ?QUERY_LIMIT)
+
+Limit the quantity of rows that can be loaded in an http query.
Review Comment:
Very nice, that makes sense
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