9 个回答
TSDB和OLAP的引擎详细区别是什么
DolphinDB的OLAP引擎，是列式存储。文件组织上，以列为单位，一个分区里的每一列，是一个文件。对于宽表只读取某列做聚合分析时，列式存储的优势能体现出来。但是对于数据的点查，OLAP引擎依旧需要把整列文件读取出来，并在内存里做计算，这个会存在点查性能差的情况。同时，对于数据的写入，假设1个表50列，一次写入涉及10...
回答于 2022-08-24 17:45
Need explanation of these messages
you can use linux version to avoid such errors. windows version is not stable
回答于 2022-01-07 16:16
Error: msum(X, window, [minPeriods]). window must be at leas...
msum is an aggregate function, it can not be used with '*'.
回答于 2022-01-05 15:21
DolphinDB crashed
Set up windows to automatically create dump file when crash(https://www.meziantou.net/tip-automatically-create-a-crash-dump-file-on-error.htm), then using vscode to debug the dmp file.
回答于 2022-01-04 13:44
长时间正常写入，突然报错：openChunks failed to find enough d...
这个一般是磁盘空间不足了，低于97%的存储空间（如果有多块盘，会计算总的）。或者如果有一个节点挂掉，在创建新分区时，也会有类似报错。
回答于 2021-12-24 09:49
表中列的值为0时，怎么得到它前一行的值
参考如下实现： t1 = `T1`T2`T3`T4`T5`T6`T7s1 = `A`A`A`A`A`A`b1= 0.35 0.34 0.33 0.28 0.29 0 0.3a1 =0.34 0.33 0.32 0.3 0 0 0.31t = table(t1 as timestamp, s1 as symbol, b1 as bid, a1 as ask)select *,ffill(iif(prev(bid)==0,NULL,prev(bid))) as last_bid, ffill(iif(prev(bid)==0,NULL,prev(timestamp))) as l...
回答于 2021-11-10 15:07
What should I do if I want to load a csv file with a column...
assume the csv file is "/home/jinzhi/Desktop/test.csv" login("admin","123456") db= database("dfs://tstdb", VALUE, 2000.01.01..2001.01.01) nameCol = `date`askO`askH`askL`askC`bidO`bidH`bidL`bidC`source`symbol; typeCol = `DATE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`SYMBOL`SYMBOL sche...
回答于 2021-10-28 15:49