[DocDB] Select statement may return stale results if fast backward scan is used

[arybochkin]

Jira Link: DB-13007

Description

An intent could be skipped during fetching a table row in case of fast backward scan enabled and a transaction with snapshot isolation level, where the given intent is not yet applied but already committed. This could lead to a stale result of a select statement (it could return old or null values).

The issue was captured by a set of tests PgSingleTServerTest/PgFastBackwardScanTest.Simple*/Fast_*_kNone

Examples of failures:

../../src/yb/yql/pgwrapper/pg_single_tserver-test.cc:883
Failed
Bad status: Illegal state (yb/yql/pgwrapper/pg_single_tserver-test.cc:785): Unexpected result: 256, 260, 5; 256, 260, 4; NULL, 5, 3; NULL, 5, 2; 4096, 5, 1 vs 256, 260, 5; 256, 260, 4; 16384, 16388, 3; NULL, 5, 2; 4096, 5, 1

../../src/yb/yql/pgwrapper/pg_single_tserver-test.cc:902
Failed
Bad status: Illegal state (yb/yql/pgwrapper/pg_single_tserver-test.cc:785): Unexpected result: NULL, 5, 2; 4096, 5, 1; NULL, NULL, 0 vs NULL, 5, 2; 4096, 5, 1; 65536, 65540, 0

Stability history Trends

Issue Type

kind/bug

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[arybochkin]

Other tests for non-packed row case (kNone) seems also flaky and fail at the same lines: PgSingleTServerTest/PgFastBackwardScanTest.Simple/Fast_WithoutNulls_kNone (link) PgSingleTServerTest/PgFastBackwardScanTest.SimpleColocated/Fast_WithNulls_kNone (link) PgSingleTServerTest/PgFastBackwardScanTest.SimpleColocated/Fast_WithoutNulls_kNone (link)