Redis Streams inconsistent behavior of blocking XREAD after XDEL - redis

Question

Calling XREAD after XDEL will not block on the stream, but return immediately. Expected behavior is for XREAD to block again.
127.0.0.1:6379> XADD my-stream * field1 string1
"1554300150697-0"
127.0.0.1:6379> XREAD BLOCK 5000 STREAMS my-stream 1554300150697-0
(nil)
(5.07s)
127.0.0.1:6379> XADD my-stream * field2 string2
"1554300285984-0"
127.0.0.1:6379> XREAD BLOCK 5000 STREAMS my-stream 1554300150697-0
1) 1) "my-stream"
2) 1) 1) "1554300285984-0"
2) 1) "field2"
2) "string2"
127.0.0.1:6379> XDEL my-stream 1554300285984-0
(integer) 1
127.0.0.1:6379> XLEN my-stream
(integer) 1
127.0.0.1:6379> XREAD BLOCK 5000 STREAMS my-stream 1554300150697-0
1) 1) "my-stream"
2) (empty list or set)
127.0.0.1:6379>
As you can see above, the first time XREAD is called it blocks for 5s - expected.
The second call to XREAD returns immediately, giving the new entry - expected.
The third call to XREAD return immediately with (empty list or set) - not expected!
Expected: The command should block for 5s.
I'm not sure if this is a bug or if there's something that I'm missing out. Please advise.
Thank you

Answer 1

It looks like you're running into this known bug.
See the second comment in particular, which points out that the partial fix supplied does not fix the issue you're running into:
It's not an entire fix for the blocking issue, since it only fixes the blocking behaviour for empty streams.
If the stream still contains some entries, but none with a larger ID than requested by the last-received-id parameter, then the request is still answered synchronously with an empty result list.

Answer 2

Looking through 5.0.4's source code I've found a way to (re)set ->last_id member through an undocumented command: XSETID
Although in the source code https://github.com/antirez/redis/blob/f72f4ea311d31f7ce209218a96afb97490971d39/src/t_stream.c#L1837 it says the syntax is XSETID <stream> <groupname> <id>, it's in fact XSETID <stream> <id>(there's an open issue on this one: https://github.com/antirez/redis/issues/5519 but I hope they'd add a new command for groups, like XGROUPSETID, and let this one as it is), which was exactly what I was looking for, so doing:
XSETID my-stream 1554300150697-0
would make:
127.0.0.1:6379> XREAD BLOCK 5000 STREAMS my-stream 1554300150697-0
(nil)
(5.08s)
127.0.0.1:6379>
to work as expected - it will block.
For anyone using this solution(which is more like a workaround in my opinion): Please use it with caution because in a high throughput machine/system/environment Redis could generate/add a new my-stream entry with the same ID as the deleted one 1554300285984-0 leading to possible duplicate data on client's side.