Add stream consumer group lag tracking and reporting (#9127)

Adds the ability to track the lag of a consumer group (CG), that is, the number
of entries yet-to-be-delivered from the stream.

The proposed constant-time solution is in the spirit of "best-effort."

Partially addresses #8737.

## Description of approach

We add a new "entries_added" property to the stream. This starts at 0 for a new
stream and is incremented by 1 with every `XADD`.  It is essentially an all-time
counter of the entries added to the stream.

Given the stream's length and this counter value, we can trivially find the logical
"entries_added" counter of the first ID if and only if the stream is contiguous.
A fragmented stream contains one or more tombstones generated by `XDEL`s.
The new "xdel_max_id" stream property tracks the latest tombstone.

The CG also tracks its last delivered ID's as an "entries_read" counter and
increments it independently when delivering new messages, unless the this
read counter is invalid (-1 means invalid offset). When the CG's counter is
available, the reported lag is the difference between added and read counters.

Lastly, this also adds a "first_id" field to the stream structure in order to make
looking it up cheaper in most cases.

## Limitations

There are two cases in which the mechanism isn't able to track the lag.
In these cases, `XINFO` replies with `null` in the "lag" field.

The first case is when a CG is created with an arbitrary last delivered ID,
that isn't "0-0", nor the first or the last entries of the stream. In this case,
it is impossible to obtain a valid read counter (short of an O(N) operation).
The second case is when there are one or more tombstones fragmenting
the stream's entries range.

In both cases, given enough time and assuming that the consumers are
active (reading and lacking) and advancing, the CG should be able to
catch up with the tip of the stream and report zero lag.
Once that's achieved, lag tracking would resume as normal (until the
next tombstone is set).

## API changes

* `XGROUP CREATE` added with the optional named argument `[ENTRIESREAD entries-read]`
  for explicitly specifying the new CG's counter.
* `XGROUP SETID` added with an optional positional argument `[ENTRIESREAD entries-read]`
  for specifying the CG's counter.
* `XINFO` reports the maximal tombstone ID, the recorded first entry ID, and total
  number of entries added to the stream.
* `XINFO` reports the current lag and logical read counter of CGs.
* `XSETID` is an internal command that's used in replication/aof. It has been added with
  the optional positional arguments `[ENTRIESADDED entries-added] [MAXDELETEDID max-deleted-entry-id]`
  for propagating the CG's offset and maximal tombstone ID of the stream.

## The generic unsolved problem

The current stream implementation doesn't provide an efficient way to obtain the
approximate/exact size of a range of entries. While it could've been nice to have
that ability (#5813) in general, let alone specifically in the context of CGs, the risk
and complexities involved in such implementation are in all likelihood prohibitive.

## A refactoring note

The `streamGetEdgeID` has been refactored to accommodate both the existing seek
of any entry as well as seeking non-deleted entries (the addition of the `skip_tombstones`
argument). Furthermore, this refactoring also migrated the seek logic to use the
`streamIterator` (rather than `raxIterator`) that was, in turn, extended with the
`skip_tombstones` Boolean struct field to control the emission of these.

Co-authored-by: Guy Benoish <guy.benoish@redislabs.com>
Co-authored-by: Oran Agra <oran@redislabs.com>

3 files changed, 271 insertions, 22 deletions

diff --git a/tests/integration/corrupt-dump.tcl b/tests/integration/corrupt-dump.tcl
index 86c7dd246..d2491306a 100644
--- a/tests/integration/corrupt-dump.tcl
+++ b/tests/integration/corrupt-dump.tcl
@@ -193,9 +193,8 @@ test {corrupt payload: listpack invalid size header} {
 test {corrupt payload: listpack too long entry len} {
     start_server [list overrides [list loglevel verbose use-exit-on-panic yes crash-memcheck-enabled no] ] {
         r config set sanitize-dump-payload no
-        r restore key 0 "\x0F\x01\x10\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x02\x40\x55\x55\x00\x00\x00\x0F\x00\x01\x01\x00\x01\x02\x01\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x00\x01\x00\x01\x00\x01\x00\x01\x02\x02\x89\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x61\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x88\x62\x00\x00\x00\x00\x00\x00\x00\x09\x08\x01\xFF\x0A\x01\x00\x00\x09\x00\x40\x63\xC9\x37\x03\xA2\xE5\x68"
         catch {
-            r xinfo stream key full
+            r restore key 0 "\x0F\x01\x10\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x02\x40\x55\x55\x00\x00\x00\x0F\x00\x01\x01\x00\x01\x02\x01\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x00\x01\x00\x01\x00\x01\x00\x01\x02\x02\x89\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x61\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x88\x62\x00\x00\x00\x00\x00\x00\x00\x09\x08\x01\xFF\x0A\x01\x00\x00\x09\x00\x40\x63\xC9\x37\x03\xA2\xE5\x68"
         } err
         assert_equal [count_log_message 0 "crashed by signal"] 0
         assert_equal [count_log_message 0 "ASSERTION FAILED"] 1
@@ -205,9 +204,9 @@ test {corrupt payload: listpack too long entry len} {
 test {corrupt payload: listpack very long entry len} {
     start_server [list overrides [list loglevel verbose use-exit-on-panic yes crash-memcheck-enabled no] ] {
         r config set sanitize-dump-payload no
-        r restore key 0 "\x0F\x01\x10\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x02\x40\x55\x55\x00\x00\x00\x0F\x00\x01\x01\x00\x01\x02\x01\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x00\x01\x00\x01\x00\x01\x00\x01\x02\x02\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x61\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x9C\x62\x00\x00\x00\x00\x00\x00\x00\x09\x08\x01\xFF\x0A\x01\x00\x00\x09\x00\x63\x6F\x42\x8E\x7C\xB5\xA2\x9D"
         catch {
-            r xinfo stream key full
+            # This will catch migrated payloads from v6.2.x
+            r restore key 0 "\x0F\x01\x10\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x02\x40\x55\x55\x00\x00\x00\x0F\x00\x01\x01\x00\x01\x02\x01\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x00\x01\x00\x01\x00\x01\x00\x01\x02\x02\x88\x31\x00\x00\x00\x00\x00\x00\x00\x09\x88\x61\x00\x00\x00\x00\x00\x00\x00\x09\x88\x32\x00\x00\x00\x00\x00\x00\x00\x09\x9C\x62\x00\x00\x00\x00\x00\x00\x00\x09\x08\x01\xFF\x0A\x01\x00\x00\x09\x00\x63\x6F\x42\x8E\x7C\xB5\xA2\x9D"
         } err
         assert_equal [count_log_message 0 "crashed by signal"] 0
         assert_equal [count_log_message 0 "ASSERTION FAILED"] 1
diff --git a/tests/unit/type/stream-cgroups.tcl b/tests/unit/type/stream-cgroups.tcl
index 9dadc1dc5..27cbc686e 100644
--- a/tests/unit/type/stream-cgroups.tcl
+++ b/tests/unit/type/stream-cgroups.tcl
@@ -623,22 +623,30 @@ start_server {
         r XDEL x 103
 
         set reply [r XINFO STREAM x FULL]
-        assert_equal [llength $reply] 12
-        assert_equal [lindex $reply 1] 4 ;# stream length
-        assert_equal [lindex $reply 9] "{100-0 {a 1}} {101-0 {b 1}} {102-0 {c 1}} {104-0 {f 1}}" ;# entries
-        assert_equal [lindex $reply 11 0 1] "g1" ;# first group name
-        assert_equal [lindex $reply 11 0 7 0 0] "100-0" ;# first entry in group's PEL
-        assert_equal [lindex $reply 11 0 9 0 1] "Alice" ;# first consumer
-        assert_equal [lindex $reply 11 0 9 0 7 0 0] "100-0" ;# first entry in first consumer's PEL
-        assert_equal [lindex $reply 11 1 1] "g2" ;# second group name
-        assert_equal [lindex $reply 11 1 9 0 1] "Charlie" ;# first consumer
-        assert_equal [lindex $reply 11 1 9 0 7 0 0] "100-0" ;# first entry in first consumer's PEL
-        assert_equal [lindex $reply 11 1 9 0 7 1 0] "101-0" ;# second entry in first consumer's PEL
+        assert_equal [llength $reply] 18
+        assert_equal [dict get $reply length] 4
+        assert_equal [dict get $reply entries] "{100-0 {a 1}} {101-0 {b 1}} {102-0 {c 1}} {104-0 {f 1}}"
+
+        # First consumer group
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group name] "g1"
+        assert_equal [lindex [dict get $group pending] 0 0] "100-0"
+        set consumer [lindex [dict get $group consumers] 0]
+        assert_equal [dict get $consumer name] "Alice"
+        assert_equal [lindex [dict get $consumer pending] 0 0] "100-0" ;# first entry in first consumer's PEL
+
+        # Second consumer group
+        set group [lindex [dict get $reply groups] 1]
+        assert_equal [dict get $group name] "g2"
+        set consumer [lindex [dict get $group consumers] 0]
+        assert_equal [dict get $consumer name] "Charlie"
+        assert_equal [lindex [dict get $consumer pending] 0 0] "100-0" ;# first entry in first consumer's PEL
+        assert_equal [lindex [dict get $consumer pending] 1 0] "101-0" ;# second entry in first consumer's PEL
 
         set reply [r XINFO STREAM x FULL COUNT 1]
-        assert_equal [llength $reply] 12
-        assert_equal [lindex $reply 1] 4
-        assert_equal [lindex $reply 9] "{100-0 {a 1}}"
+        assert_equal [llength $reply] 18
+        assert_equal [dict get $reply length] 4
+        assert_equal [dict get $reply entries] "{100-0 {a 1}}"
     }
 
     test {XGROUP CREATECONSUMER: create consumer if does not exist} {
@@ -702,7 +710,7 @@ start_server {
             set grpinfo [r xinfo groups mystream]
 
             r debug loadaof
-            assert {[r xinfo groups mystream] == $grpinfo}
+            assert_equal [r xinfo groups mystream] $grpinfo
             set reply [r xinfo consumers mystream mygroup]
             set consumer_info [lindex $reply 0]
             assert_equal [lindex $consumer_info 1] "Alice" ;# consumer name
@@ -741,6 +749,154 @@ start_server {
         }
     }
 
+    test {Consumer group read counter and lag in empty streams} {
+        r DEL x
+        r XGROUP CREATE x g1 0 MKSTREAM
+
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $reply max-deleted-entry-id] "0-0"
+        assert_equal [dict get $reply entries-added] 0
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] 0
+
+        r XADD x 1-0 data a
+        r XDEL x 1-0
+
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $reply max-deleted-entry-id] "1-0"
+        assert_equal [dict get $reply entries-added] 1
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] 0
+    }
+
+    test {Consumer group read counter and lag sanity} {
+        r DEL x
+        r XADD x 1-0 data a
+        r XADD x 2-0 data b
+        r XADD x 3-0 data c
+        r XADD x 4-0 data d
+        r XADD x 5-0 data e
+        r XGROUP CREATE x g1 0
+
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] 5
+
+        r XREADGROUP GROUP g1 c11 COUNT 1 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 1
+        assert_equal [dict get $group lag] 4
+
+        r XREADGROUP GROUP g1 c12 COUNT 10 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 0
+
+        r XADD x 6-0 data f
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 1
+    }
+
+    test {Consumer group lag with XDELs} {
+        r DEL x
+        r XADD x 1-0 data a
+        r XADD x 2-0 data b
+        r XADD x 3-0 data c
+        r XADD x 4-0 data d
+        r XADD x 5-0 data e
+        r XDEL x 3-0
+        r XGROUP CREATE x g1 0
+        r XGROUP CREATE x g2 0
+        
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] {}
+
+        r XREADGROUP GROUP g1 c11 COUNT 1 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] {}
+
+        r XREADGROUP GROUP g1 c11 COUNT 1 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] {}
+
+        r XREADGROUP GROUP g1 c11 COUNT 1 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] {}
+
+        r XREADGROUP GROUP g1 c11 COUNT 1 STREAMS x >
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 0
+
+        r XADD x 6-0 data f
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 1
+        
+        r XTRIM x MINID = 3-0
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 1
+        set group [lindex [dict get $reply groups] 1]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] 3
+
+        r XTRIM x MINID = 5-0
+        set reply [r XINFO STREAM x FULL]
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 5
+        assert_equal [dict get $group lag] 1
+        set group [lindex [dict get $reply groups] 1]
+        assert_equal [dict get $group entries-read] {}
+        assert_equal [dict get $group lag] 2
+    }
+
+    test {Loading from legacy (Redis <= v6.2.x, rdb_ver < 10) persistence} {
+        # The payload was DUMPed from a v5 instance after:
+        # XADD x 1-0 data a
+        # XADD x 2-0 data b
+        # XADD x 3-0 data c
+        # XADD x 4-0 data d
+        # XADD x 5-0 data e
+        # XADD x 6-0 data f
+        # XDEL x 3-0
+        # XGROUP CREATE x g1 0
+        # XGROUP CREATE x g2 0
+        # XREADGROUP GROUP g1 c11 COUNT 4 STREAMS x >
+        # XTRIM x MAXLEN = 2
+
+        r DEL x
+        r RESTORE x 0 "\x0F\x01\x10\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\xC3\x40\x4A\x40\x57\x16\x57\x00\x00\x00\x23\x00\x02\x01\x04\x01\x01\x01\x84\x64\x61\x74\x61\x05\x00\x01\x03\x01\x00\x20\x01\x03\x81\x61\x02\x04\x20\x0A\x00\x01\x40\x0A\x00\x62\x60\x0A\x00\x02\x40\x0A\x00\x63\x60\x0A\x40\x22\x01\x81\x64\x20\x0A\x40\x39\x20\x0A\x00\x65\x60\x0A\x00\x05\x40\x0A\x00\x66\x20\x0A\x00\xFF\x02\x06\x00\x02\x02\x67\x31\x05\x00\x04\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x3E\xF7\x83\x43\x7A\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x3E\xF7\x83\x43\x7A\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x3E\xF7\x83\x43\x7A\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x05\x00\x00\x00\x00\x00\x00\x00\x00\x3E\xF7\x83\x43\x7A\x01\x00\x00\x01\x01\x03\x63\x31\x31\x3E\xF7\x83\x43\x7A\x01\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x05\x00\x00\x00\x00\x00\x00\x00\x00\x02\x67\x32\x00\x00\x00\x00\x09\x00\x3D\x52\xEF\x68\x67\x52\x1D\xFA"
+
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply max-deleted-entry-id] "0-0"
+        assert_equal [dict get $reply entries-added] 2
+        set group [lindex [dict get $reply groups] 0]
+        assert_equal [dict get $group entries-read] 1
+        assert_equal [dict get $group lag] 1
+        set group [lindex [dict get $reply groups] 1]
+        assert_equal [dict get $group entries-read] 0
+        assert_equal [dict get $group lag] 2
+    }
+
     start_server {tags {"external:skip"}} {
         set master [srv -1 client]
         set master_host [srv -1 host]
@@ -841,7 +997,7 @@ start_server {
             waitForBgrewriteaof r
             r debug loadaof
             assert {[dict get [r xinfo stream mystream] length] == 0}
-            assert {[r xinfo groups mystream] == $grpinfo}
+            assert_equal [r xinfo groups mystream] $grpinfo
         }
     }
 }
diff --git a/tests/unit/type/stream.tcl b/tests/unit/type/stream.tcl
index 7ba3ed116..bd689cd29 100644
--- a/tests/unit/type/stream.tcl
+++ b/tests/unit/type/stream.tcl
@@ -760,7 +760,9 @@ start_server {tags {"stream xsetid"}} {
 
     test {XSETID can set a specific ID} {
         r XSETID mystream "200-0"
-        assert {[dict get [r xinfo stream mystream] last-generated-id] == "200-0"}
+        set reply [r XINFO stream mystream]
+        assert_equal [dict get $reply last-generated-id] "200-0"
+        assert_equal [dict get $reply entries-added] 1
     }
 
     test {XSETID cannot SETID with smaller ID} {
@@ -774,6 +776,98 @@ start_server {tags {"stream xsetid"}} {
         catch {r XSETID stream 1-1} err
         set _ $err
     } {ERR no such key}
+
+    test {XSETID cannot run with an offset but without a maximal tombstone} {
+        catch {r XSETID stream 1-1 0} err
+        set _ $err
+    } {ERR syntax error}
+
+    test {XSETID cannot run with a maximal tombstone but without an offset} {
+        catch {r XSETID stream 1-1 0-0} err
+        set _ $err
+    } {ERR syntax error}
+
+    test {XSETID errors on negstive offset} {
+        catch {r XSETID stream 1-1 ENTRIESADDED -1 MAXDELETEDID 0-0} err
+        set _ $err
+    } {ERR*must be positive}
+
+    test {XSETID cannot set the maximal tombstone with larger ID} {
+        r DEL x
+        r XADD x 1-0 a b
+        
+        catch {r XSETID x "1-0" ENTRIESADDED 1 MAXDELETEDID "2-0" } err
+        r XADD mystream MAXLEN 0 * a b
+        set err
+    } {ERR*smaller*}
+
+    test {XSETID cannot set the offset to less than the length} {
+        r DEL x
+        r XADD x 1-0 a b
+        
+        catch {r XSETID x "1-0" ENTRIESADDED 0 MAXDELETEDID "0-0" } err
+        r XADD mystream MAXLEN 0 * a b
+        set err
+    } {ERR*smaller*}
+}
+
+start_server {tags {"stream offset"}} {
+    test {XADD advances the entries-added counter and sets the recorded-first-entry-id} {
+        r DEL x
+        r XADD x 1-0 data a
+
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply entries-added] 1
+        assert_equal [dict get $reply recorded-first-entry-id] "1-0"
+
+        r XADD x 2-0 data a
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply entries-added] 2
+        assert_equal [dict get $reply recorded-first-entry-id] "1-0"
+    }
+
+    test {XDEL/TRIM are reflected by recorded first entry} {
+        r DEL x
+        r XADD x 1-0 data a
+        r XADD x 2-0 data a
+        r XADD x 3-0 data a
+        r XADD x 4-0 data a
+        r XADD x 5-0 data a
+
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply entries-added] 5
+        assert_equal [dict get $reply recorded-first-entry-id] "1-0"
+
+        r XDEL x 2-0
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply recorded-first-entry-id] "1-0"
+
+        r XDEL x 1-0
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply recorded-first-entry-id] "3-0"
+
+        r XTRIM x MAXLEN = 2
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply recorded-first-entry-id] "4-0"
+    }
+
+    test {Maxmimum XDEL ID behaves correctly} {
+        r DEL x
+        r XADD x 1-0 data a
+        r XADD x 2-0 data b
+        r XADD x 3-0 data c
+
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply max-deleted-entry-id] "0-0"
+
+        r XDEL x 2-0
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply max-deleted-entry-id] "2-0"
+
+        r XDEL x 1-0
+        set reply [r XINFO STREAM x FULL]
+        assert_equal [dict get $reply max-deleted-entry-id] "2-0"
+    }
 }
 
 start_server {tags {"stream needs:debug"} overrides {appendonly yes aof-use-rdb-preamble no}} {
@@ -796,7 +890,7 @@ start_server {tags {"stream needs:debug"} overrides {appendonly yes aof-use-rdb-
         waitForBgrewriteaof r
         r debug loadaof
         assert {[dict get [r xinfo stream mystream] length] == 1}
-        assert {[dict get [r xinfo stream mystream] last-generated-id] == "2-2"}
+        assert_equal [dict get [r xinfo stream mystream] last-generated-id] "2-2"
     }
 }