html_url,issue_url,id,node_id,user,user_label,created_at,updated_at,author_association,body,reactions,issue,issue_label,performed_via_github_app
https://github.com/simonw/datasette/issues/1679#issuecomment-1074331743,https://api.github.com/repos/simonw/datasette/issues/1679,1074331743,IC_kwDOBm6k_c5ACQBf,9599,simonw,2022-03-21T19:30:05Z,2022-03-21T19:30:05Z,OWNER,"https://github.com/simonw/datasette/blob/1a7750eb29fd15dd2eea3b9f6e33028ce441b143/datasette/app.py#L118-L122 sets it to 50ms for facet suggestion but that's not going to pass `ms < 50`:
```python
Setting(
""facet_suggest_time_limit_ms"",
50,
""Time limit for calculating a suggested facet"",
),
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074332325,https://api.github.com/repos/simonw/datasette/issues/1679,1074332325,IC_kwDOBm6k_c5ACQKl,9599,simonw,2022-03-21T19:30:44Z,2022-03-21T19:30:44Z,OWNER,So it looks like even for facet suggestion `n=1000` always - it's never reduced to `n=1`.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074332718,https://api.github.com/repos/simonw/datasette/issues/1679,1074332718,IC_kwDOBm6k_c5ACQQu,9599,simonw,2022-03-21T19:31:10Z,2022-03-21T19:31:10Z,OWNER,How long does it take for SQLite to execute 1000 opcodes anyway?,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074337997,https://api.github.com/repos/simonw/datasette/issues/1679,1074337997,IC_kwDOBm6k_c5ACRjN,9599,simonw,2022-03-21T19:37:08Z,2022-03-21T19:37:08Z,OWNER,"This is weird:
```python
import sqlite3
db = sqlite3.connect("":memory:"")
i = 0
def count():
global i
i += 1
db.set_progress_handler(count, 1)
db.execute(""""""
with recursive counter(x) as (
select 0
union
select x + 1 from counter
)
select * from counter limit 10000;
"""""")
print(i)
```
Outputs `24`. But if you try the same thing in the SQLite console:
```
sqlite> .stats vmstep
sqlite> with recursive counter(x) as (
...> select 0
...> union
...> select x + 1 from counter
...> )
...> select * from counter limit 10000;
...
VM-steps: 200007
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074341924,https://api.github.com/repos/simonw/datasette/issues/1679,1074341924,IC_kwDOBm6k_c5ACSgk,9599,simonw,2022-03-21T19:42:08Z,2022-03-21T19:42:08Z,OWNER,"Here's the Python-C implementation of `set_progress_handler`: https://github.com/python/cpython/blob/4674fd4e938eb4a29ccd5b12c15455bd2a41c335/Modules/_sqlite/connection.c#L1177-L1201
It calls `sqlite3_progress_handler(self->db, n, progress_callback, ctx);`
https://www.sqlite.org/c3ref/progress_handler.html says:
> The parameter N is the approximate number of [virtual machine instructions](https://www.sqlite.org/opcode.html) that are evaluated between successive invocations of the callback X
So maybe VM-steps and virtual machine instructions are different things?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074347023,https://api.github.com/repos/simonw/datasette/issues/1679,1074347023,IC_kwDOBm6k_c5ACTwP,9599,simonw,2022-03-21T19:48:59Z,2022-03-21T19:48:59Z,OWNER,Posed a question about that here: https://sqlite.org/forum/forumpost/de9ff10fa7,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074439309,https://api.github.com/repos/simonw/datasette/issues/1679,1074439309,IC_kwDOBm6k_c5ACqSN,9599,simonw,2022-03-21T21:28:58Z,2022-03-21T21:28:58Z,OWNER,"David Raymond solved it there: https://sqlite.org/forum/forumpost/330c8532d8a88bcd
> Don't forget to step through the results. All .execute() has done is prepared it.
>
> db.execute(query).fetchall()
Sure enough, adding that gets the VM steps number up to 190,007 which is close enough that I'm happy.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074446576,https://api.github.com/repos/simonw/datasette/issues/1679,1074446576,IC_kwDOBm6k_c5ACsDw,9599,simonw,2022-03-21T21:38:27Z,2022-03-21T21:38:27Z,OWNER,"OK here's a microbenchmark script:
```python
import sqlite3
import timeit
db = sqlite3.connect("":memory:"")
db_with_progress_handler_1 = sqlite3.connect("":memory:"")
db_with_progress_handler_1000 = sqlite3.connect("":memory:"")
db_with_progress_handler_1.set_progress_handler(lambda: None, 1)
db_with_progress_handler_1000.set_progress_handler(lambda: None, 1000)
def execute_query(db):
cursor = db.execute(""""""
with recursive counter(x) as (
select 0
union
select x + 1 from counter
)
select * from counter limit 10000;
"""""")
list(cursor.fetchall())
print(""Without progress_handler"")
print(timeit.timeit(lambda: execute_query(db), number=100))
print(""progress_handler every 1000 ops"")
print(timeit.timeit(lambda: execute_query(db_with_progress_handler_1000), number=100))
print(""progress_handler every 1 op"")
print(timeit.timeit(lambda: execute_query(db_with_progress_handler_1), number=100))
```
Results:
```
% python3 bench.py
Without progress_handler
0.8789225700311363
progress_handler every 1000 ops
0.8829826560104266
progress_handler every 1 op
2.8892734259716235
```
So running every 1000 ops makes almost no difference at all, but running every single op is a 3.2x performance degradation.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074454687,https://api.github.com/repos/simonw/datasette/issues/1679,1074454687,IC_kwDOBm6k_c5ACuCf,9599,simonw,2022-03-21T21:48:02Z,2022-03-21T21:48:02Z,OWNER,"Here's another microbenchmark that measures how many nanoseconds it takes to run 1,000 vmops:
```python
import sqlite3
import time
db = sqlite3.connect("":memory:"")
i = 0
out = []
def count():
global i
i += 1000
out.append(((i, time.perf_counter_ns())))
db.set_progress_handler(count, 1000)
print(""Start:"", time.perf_counter_ns())
all = db.execute(""""""
with recursive counter(x) as (
select 0
union
select x + 1 from counter
)
select * from counter limit 10000;
"""""").fetchall()
print(""End:"", time.perf_counter_ns())
print()
print(""So how long does it take to execute 1000 ops?"")
prev_time_ns = None
for i, time_ns in out:
if prev_time_ns is not None:
print(time_ns - prev_time_ns, ""ns"")
prev_time_ns = time_ns
```
Running it:
```
% python nanobench.py
Start: 330877620374821
End: 330877632515822
So how long does it take to execute 1000 ops?
47290 ns
49573 ns
48226 ns
45674 ns
53238 ns
47313 ns
52346 ns
48689 ns
47092 ns
87596 ns
69999 ns
52522 ns
52809 ns
53259 ns
52478 ns
53478 ns
65812 ns
```
87596ns is 0.087596ms - so even a measure rate of every 1000 ops is easily finely grained enough to capture differences of less than 0.1ms.
If anything I could bump that default 1000 up - and I can definitely eliminate the `if ms < 50` branch entirely.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074458506,https://api.github.com/repos/simonw/datasette/issues/1679,1074458506,IC_kwDOBm6k_c5ACu-K,9599,simonw,2022-03-21T21:53:47Z,2022-03-21T21:53:47Z,OWNER,"Oh interesting, it turns out there is ONE place in the code that sets the `ms` to less than 20 - this test fixture: https://github.com/simonw/datasette/blob/4e47a2d894b96854348343374c8e97c9d7055cf6/tests/fixtures.py#L224-L226","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,
https://github.com/simonw/datasette/issues/1679#issuecomment-1074459746,https://api.github.com/repos/simonw/datasette/issues/1679,1074459746,IC_kwDOBm6k_c5ACvRi,9599,simonw,2022-03-21T21:55:45Z,2022-03-21T21:55:45Z,OWNER,I'm going to change the original logic to set n=1 for times that are `<= 20ms` - and update the comments to make it more obvious what is happening.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1175854982,Research: how much overhead does the n=1 time limit have?,