topic Re: Databricks write to Azure Data Explorer writes suddenly become slower in Data Engineering

Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Wed, 01 Jun 2022 07:37:41 GMT

Now, I write to Azure Data explorer using Spark streaming. one day， writes suddenly become slower. restart is no effect.

I have a questions about Spark Streaming to Azure Data explorer.

Q1: What should I do to get performance to reply?

Figure 1 shows the performance of writing in the current table.

Figure 2 the performance of writing in the now table.

Figure 3 the performance of writing in the current table, but the checkpoint location is new.

Could it be that checkpoint location caused it?

Re: Databricks write to Azure Data Explorer writes suddenly become slower

-werners- — Wed, 01 Jun 2022 12:47:30 GMT

if the checkpoint location is in another region or has another 'level' (think premium vs standard storage) that could be the case.

Can you check that?

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Thu, 02 Jun 2022 07:35:45 GMT

Thank you for your answer.

I check it.

data source（AdxDF） and checkpoint location is the same container, Only the path is different.

Azure Data Explorer and data source is the same region.

I have a new discovery.

if I write to the new table. It's fast at first, and after a few hours of running, it suddenly slows down.

I'll add a screenshot later

Re: Databricks write to Azure Data Explorer writes suddenly become slower

User16764241763 — Mon, 06 Jun 2022 03:36:16 GMT

Is it Blob storage or ADLS Storage account where your data and checkpoint files are stored?

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Mon, 06 Jun 2022 06:20:51 GMT

It's Azure Data Lake Storage Gen2.

Re: Databricks write to Azure Data Explorer writes suddenly become slower

-werners- — Tue, 07 Jun 2022 11:21:04 GMT

could it be the stream query that gets slow? Maybe checkpoint more often?

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Wed, 08 Jun 2022 01:42:02 GMT

Re: Databricks write to Azure Data Explorer writes suddenly become slower

jose_gonzalez — Fri, 29 Jul 2022 00:35:42 GMT

Do you have any more data to be process? check the driver logs for any errors messages? this suddenly drop might point to another issue happening here

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Tue, 28 Mar 2023 02:18:45 GMT

I'm so sorry, I just thought the issue wasn't resolved

Solution

Set maxFilesPerTrigger and maxBytesPerTrigger
Enable autpoptimize

Reason

for the first day, it processes larger files and then eventually process smaller files。

Detailed reason

Before performance drops：

1000 = (endOffset's index - startOffset's index) = （80999- 79999）

1305389 = numInputRows

avg records per files is 1305389/1000 = 1305.389

After performance drops：1000 = (endOffset's index - startOffset's index) = （90999- 89999）

45644= numInputRows

avg records per files is 45644/1000 = 45

From the comparison of (1) and (2), it can be seen that the number of files read by each batch before and after the performance drop (23:30) remains unchanged at 1000, but after 23:30 the number of 1000 total files changes. Less, it is most likely that the file size has become smaller, resulting in a smaller file, so the total number of read items has decreased. That is, for the first day, it processes larger files and then eventually processes smaller files.

Suggestion：

https://docs.microsoft.com/en-gb/azure/databricks/delta/delta-streaming#limit-input-rate

https://docs.microsoft.com/en-us/azure/databricks/delta/optimizations/auto-optimize

Finally, a big thank you to the Databricks team and the Microsoft team for their technical support.

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Tue, 28 Mar 2023 02:22:42 GMT

I'm very sorry to reply you now, this problem has been resolved, the specific reason is in another answer.

Re: Databricks write to Azure Data Explorer writes suddenly become slower

RengarLee — Tue, 28 Mar 2023 02:22:49 GMT

I'm very sorry to reply you now, this problem has been resolved, the specific reason is in another answer.