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[DocDB] Flush regular db immediate if intents db write is blocked by immutable mem tables #18358

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spolitov opened this issue Jul 21, 2023 · 0 comments
Closed
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[DocDB] Flush regular db immediate if intents db write is blocked by immutable mem tables #18358

spolitov opened this issue Jul 21, 2023 · 0 comments
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area/docdb YugabyteDB core features kind/enhancement This is an enhancement of an existing feature priority/medium Medium priority issue

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spolitov commented Jul 21, 2023 •
edited by jira bot

Jira Link: DB-7343

Description

We cannot flush intents db before regular db, since it could result in situation when intents were deleted from intents db.
But transaction was not yet applied to regular db.
So there is a logic to postpone intents db flush until regular db is flushed.

RocksDB rejects new writes when there are too many non flushed mem tables.
In our system it is configured to 2 mem tables.

So we could get into situation when writes are blocked because there are too many non flushed mem tables in intents db.
But intents db waits until regular db is flushed.

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@spolitov spolitov added area/docdb YugabyteDB core features status/awaiting-triage Issue awaiting triage labels Jul 21, 2023
@spolitov spolitov self-assigned this Jul 21, 2023
@yugabyte-ci yugabyte-ci added kind/enhancement This is an enhancement of an existing feature priority/medium Medium priority issue labels Jul 21, 2023
spolitov added a commit that referenced this issue Jul 24, 2023
@spolitov
[#18358] DocDB: Flush regular db immediate if intents db write is blo…
a25e408 
…cked by immutable mem tables

Summary:
We cannot flush intents db before regular db, since it could result in situation when intents were deleted from intents db.
But transaction was not yet applied to regular db.
So there is a logic to postpone intents db flush until regular db is flushed.

RocksDB rejects new writes when there are too many non flushed mem tables.
In our system it is configured to 2 mem tables.

We could get into situation when writes are blocked because there are too many non flushed mem tables in intents db.
But intents db waits until regular db is flushed.
So write will blocked for 2 second, until we flush regular db because of `intents_flush_max_delay_ms`.

The issue was found when I was working on new test PgSingleTServerTest.ScanComplexPK.
Without this fix, test execution time in release mode is 90s+.
With this fix, test execution time in release mode is 50s-.
Jira: DB-7343

Test Plan: PgSingleTServerTest.ScanComplexPK

Reviewers: bogdan, rthallam

Reviewed By: bogdan

Subscribers: yql, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D27163
@yugabyte-ci yugabyte-ci removed the status/awaiting-triage Issue awaiting triage label Jul 25, 2023
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