我有一個數據庫表示安全攝像機NVR的元數據。每1分鐘視頻段有一個26字節的recording
行。 (如果您好奇,設計文檔正在進行中here。)我的設計限制是8個攝像頭,1年(約400萬行,每個攝像頭50萬)。我僞裝了一些數據來測試性能。此查詢比我預期的要慢:這個SQLite查詢可以做得更快嗎?
select
recording.start_time_90k,
recording.duration_90k,
recording.video_samples,
recording.sample_file_bytes,
recording.video_sample_entry_id
from
recording
where
camera_id = ?
order by
recording.start_time_90k;
這只是掃描攝像機的所有數據,使用索引過濾掉其他攝像機和訂購。指數如下:
create index recording_camera_start on recording (camera_id, start_time_90k);
explain query plan
看起來預期:
0|0|0|SEARCH TABLE recording USING INDEX recording_camera_start (camera_id=?)
的行是相當小的。
$ sqlite3_analyzer duplicated.db
...
*** Table RECORDING w/o any indices *******************************************
Percentage of total database...................... 66.3%
Number of entries................................. 4225560
Bytes of storage consumed......................... 143418368
Bytes of payload.................................. 109333605 76.2%
B-tree depth...................................... 4
Average payload per entry......................... 25.87
Average unused bytes per entry.................... 0.99
Average fanout.................................... 94.00
Non-sequential pages.............................. 1 0.0%
Maximum payload per entry......................... 26
Entries that use overflow......................... 0 0.0%
Index pages used.................................. 1488
Primary pages used................................ 138569
Overflow pages used............................... 0
Total pages used.................................. 140057
Unused bytes on index pages....................... 188317 12.4%
Unused bytes on primary pages..................... 3987216 2.8%
Unused bytes on overflow pages.................... 0
Unused bytes on all pages......................... 4175533 2.9%
*** Index RECORDING_CAMERA_START of table RECORDING ***************************
Percentage of total database...................... 33.7%
Number of entries................................. 4155718
Bytes of storage consumed......................... 73003008
Bytes of payload.................................. 58596767 80.3%
B-tree depth...................................... 4
Average payload per entry......................... 14.10
Average unused bytes per entry.................... 0.21
Average fanout.................................... 49.00
Non-sequential pages.............................. 1 0.001%
Maximum payload per entry......................... 14
Entries that use overflow......................... 0 0.0%
Index pages used.................................. 1449
Primary pages used................................ 69843
Overflow pages used............................... 0
Total pages used.................................. 71292
Unused bytes on index pages....................... 8463 0.57%
Unused bytes on primary pages..................... 865598 1.2%
Unused bytes on overflow pages.................... 0
Unused bytes on all pages......................... 874061 1.2%
...
我想是這樣的(也許只用了一個月的時間,而不是滿一年)要運行的每一個特定的網頁被打的時候,所以我想這是相當快的。但在我的筆記本電腦上,它需要大部分時間,並且我希望支持Raspberry Pi 2,但速度太慢。下面的時間(以秒爲單位);它是CPU綁定的(用戶+ SYS時間〜=實時):
laptop$ time ./bench-profiled
trial 0: time 0.633 sec
trial 1: time 0.636 sec
trial 2: time 0.639 sec
trial 3: time 0.679 sec
trial 4: time 0.649 sec
trial 5: time 0.642 sec
trial 6: time 0.609 sec
trial 7: time 0.640 sec
trial 8: time 0.666 sec
trial 9: time 0.715 sec
...
PROFILE: interrupts/evictions/bytes = 1974/489/72648
real 0m20.546s
user 0m16.564s
sys 0m3.976s
(This is Ubuntu 15.10, SQLITE_VERSION says "3.8.11.1")
raspberrypi2$ time ./bench-profiled
trial 0: time 6.334 sec
trial 1: time 6.216 sec
trial 2: time 6.364 sec
trial 3: time 6.412 sec
trial 4: time 6.398 sec
trial 5: time 6.389 sec
trial 6: time 6.395 sec
trial 7: time 6.424 sec
trial 8: time 6.391 sec
trial 9: time 6.396 sec
...
PROFILE: interrupts/evictions/bytes = 19066/2585/43124
real 3m20.083s
user 2m47.120s
sys 0m30.620s
(This is Raspbian Jessie; SQLITE_VERSION says "3.8.7.1")
我很可能會最終做某種非規範化的數據,但首先我想看看我是否能得到這個簡單的查詢表現的很好。我的基準很簡單,它準備的聲明提前,然後遍歷這個:
void Trial(sqlite3_stmt *stmt) {
int ret;
while ((ret = sqlite3_step(stmt)) == SQLITE_ROW) ;
if (ret != SQLITE_DONE) {
errx(1, "sqlite3_step: %d (%s)", ret, sqlite3_errstr(ret));
}
ret = sqlite3_reset(stmt);
if (ret != SQLITE_OK) {
errx(1, "sqlite3_reset: %d (%s)", ret, sqlite3_errstr(ret));
}
}
我做了一個CPU配置文件與gperftools。圖片:
$ google-pprof bench-profiled timing.pprof
Using local file bench-profiled.
Using local file timing.pprof.
Welcome to pprof! For help, type 'help'.
(pprof) top 10
Total: 593 samples
154 26.0% 26.0% 377 63.6% sqlite3_randomness
134 22.6% 48.6% 557 93.9% sqlite3_reset
83 14.0% 62.6% 83 14.0% __read_nocancel
61 10.3% 72.8% 61 10.3% sqlite3_strnicmp
41 6.9% 79.8% 46 7.8% sqlite3_free_table
26 4.4% 84.1% 26 4.4% sqlite3_uri_parameter
25 4.2% 88.4% 25 4.2% llseek
13 2.2% 90.6% 121 20.4% sqlite3_db_config
12 2.0% 92.6% 12 2.0% __pthread_mutex_unlock_usercnt (inline)
10 1.7% 94.3% 10 1.7% __GI___pthread_mutex_lock
這看起來自嘆不如給我希望它能夠得到改善。也許我在做一些愚蠢的事情。我特別懷疑的sqlite3_randomness和sqlite3_strnicmp操作:
- 文檔說
sqlite3_randomness
用於在某些情況下,插入的rowid,但我只是做一個選擇查詢。爲什麼現在要使用它?從瀏覽sqlite3源代碼,我發現它用於選擇sqlite3ColumnsFromExprList
,但似乎是準備語句時會發生的事情。我只做過一次,而不是被基準測試的部分。 strnicmp
用於不區分大小寫的字符串比較。但是這個表中的每個字段都是一個整數。爲什麼會使用這個功能?它是什麼比較?- 並且一般來說,我不知道爲什麼
sqlite3_reset
會很貴,或者爲什麼會從sqlite3_step
中調用。
模式:
-- Each row represents a single recorded segment of video.
-- Segments are typically ~60 seconds; never more than 5 minutes.
-- Each row should have a matching recording_detail row.
create table recording (
id integer primary key,
camera_id integer references camera (id) not null,
sample_file_bytes integer not null check (sample_file_bytes > 0),
-- The starting time of the recording, in 90 kHz units since
-- 1970-01-01 00:00:00 UTC.
start_time_90k integer not null check (start_time_90k >= 0),
-- The duration of the recording, in 90 kHz units.
duration_90k integer not null
check (duration_90k >= 0 and duration_90k < 5*60*90000),
video_samples integer not null check (video_samples > 0),
video_sync_samples integer not null check (video_samples > 0),
video_sample_entry_id integer references video_sample_entry (id)
);
我柏油了我的測試數據+測試程序;你可以下載它here。
編輯1:
啊,通過SQLite的代碼看,我看到了一個線索:
int sqlite3_step(sqlite3_stmt *pStmt){
int rc = SQLITE_OK; /* Result from sqlite3Step() */
int rc2 = SQLITE_OK; /* Result from sqlite3Reprepare() */
Vdbe *v = (Vdbe*)pStmt; /* the prepared statement */
int cnt = 0; /* Counter to prevent infinite loop of reprepares */
sqlite3 *db; /* The database connection */
if(vdbeSafetyNotNull(v)){
return SQLITE_MISUSE_BKPT;
}
db = v->db;
sqlite3_mutex_enter(db->mutex);
v->doingRerun = 0;
while((rc = sqlite3Step(v))==SQLITE_SCHEMA
&& cnt++ < SQLITE_MAX_SCHEMA_RETRY){
int savedPc = v->pc;
rc2 = rc = sqlite3Reprepare(v);
if(rc!=SQLITE_OK) break;
sqlite3_reset(pStmt);
if(savedPc>=0) v->doingRerun = 1;
assert(v->expired==0);
}
它看起來像sqlite3_step
電話sqlite3_reset
的模式更改。 (FAQ entry)我不知道爲什麼,因爲我的發言雖然準備有會是一個架構更改...
編輯2:
我下載了SQLite的3.10.1「amalgation 「並通過調試符號進行編譯。現在我看到一個非常不同的配置文件,看起來並不奇怪,但它並沒有更快。也許我之前看到的奇怪的結果是由於相同的代碼摺疊或某事。
編輯3:
下面試圖奔的聚簇索引的解決方案,它是關於3.6X更快。我認爲這是我要用這個查詢做的最好的。 SQLite的CPU性能在筆記本電腦上約爲700 MB/s。在重寫它爲其虛擬機或類似應用程序使用JIT編譯器的時候,我不會做得更好。特別是,我認爲我在我的第一個檔案中看到的怪異電話實際上並沒有發生,由於優化等原因,gcc必須編寫誤導性的調試信息。
即使CPU性能會得到改善,吞吐量也會超過我的存儲在冷讀時所能做到的,我認爲Pi也是如此(它的SD卡有一個有限的USB 2.0總線) 。
$ time ./bench
sqlite3 version: 3.10.1
trial 0: realtime 0.172 sec cputime 0.172 sec
trial 1: realtime 0.172 sec cputime 0.172 sec
trial 2: realtime 0.175 sec cputime 0.175 sec
trial 3: realtime 0.173 sec cputime 0.173 sec
trial 4: realtime 0.182 sec cputime 0.182 sec
trial 5: realtime 0.187 sec cputime 0.187 sec
trial 6: realtime 0.173 sec cputime 0.173 sec
trial 7: realtime 0.185 sec cputime 0.185 sec
trial 8: realtime 0.190 sec cputime 0.190 sec
trial 9: realtime 0.192 sec cputime 0.192 sec
trial 10: realtime 0.191 sec cputime 0.191 sec
trial 11: realtime 0.188 sec cputime 0.188 sec
trial 12: realtime 0.186 sec cputime 0.186 sec
trial 13: realtime 0.179 sec cputime 0.179 sec
trial 14: realtime 0.179 sec cputime 0.179 sec
trial 15: realtime 0.188 sec cputime 0.188 sec
trial 16: realtime 0.178 sec cputime 0.178 sec
trial 17: realtime 0.175 sec cputime 0.175 sec
trial 18: realtime 0.182 sec cputime 0.182 sec
trial 19: realtime 0.178 sec cputime 0.178 sec
trial 20: realtime 0.189 sec cputime 0.189 sec
trial 21: realtime 0.191 sec cputime 0.191 sec
trial 22: realtime 0.179 sec cputime 0.179 sec
trial 23: realtime 0.185 sec cputime 0.185 sec
trial 24: realtime 0.190 sec cputime 0.190 sec
trial 25: realtime 0.189 sec cputime 0.189 sec
trial 26: realtime 0.182 sec cputime 0.182 sec
trial 27: realtime 0.176 sec cputime 0.176 sec
trial 28: realtime 0.173 sec cputime 0.173 sec
trial 29: realtime 0.181 sec cputime 0.181 sec
PROFILE: interrupts/evictions/bytes = 547/178/24592
real 0m5.651s
user 0m5.292s
sys 0m0.356s
我可能需要保留一些非規範化的數據。幸運的是,我認爲我可以將它保存在應用程序的RAM中,因爲它不會太大,啓動不必非常快,並且只有一個進程寫入數據庫。
感謝您爲您的問題投入瞭如此多的研究工作!你能說出你是CPU限還是IO限?你是否在你的Raspberry Pi上使用[Class 10 SD卡](http://raspberrypi.stackexchange.com/q/12191/27703)? –
謝謝!還有一個我忘記回答的重要問題。它在兩個系統上都是CPU綁定的。我在上面添加了「時間」輸出來顯示。我正在使用Class 10 SD卡:http://www.amazon.com/gp/product/B010Q588D4?psc=1&redirect=true&ref_=od_aui_detailpages00 –
真棒問題!有了這個級別的細節,你應該也可以發佈到sqlite-users ML。 – viraptor