Commented by: @hvlad

The case was described at http://www.sql.ru/forum/1220706/upala-skorost-update-pri-perehode-s-2-5-na-3-0:

CREATE TABLE TEST_TABLE (
VALUE_1 INTEGER,
VALUE_2 INTEGER,
VALUE_3 INTEGER
);
commit;

CREATE INDEX TEST_TABLE_IDX1 ON TEST_TABLE (VALUE_1);
CREATE INDEX TEST_TABLE_IDX2 ON TEST_TABLE (VALUE_2);
CREATE INDEX TEST_TABLE_IDX3 ON TEST_TABLE (VALUE_3);
CREATE INDEX TEST_TABLE_IDX4 ON TEST_TABLE (VALUE_1, VALUE_2);
CREATE INDEX TEST_TABLE_IDX5 ON TEST_TABLE (VALUE_1, VALUE_3);
CREATE INDEX TEST_TABLE_IDX6 ON TEST_TABLE (VALUE_1, VALUE_2, VALUE_3);
commit;

SET TERM ^ ;

create procedure MAKE_UPDATES
as
declare variable i integer;
declare variable n integer;
begin
i = 0;
n = 50000;
delete from test_table;
while (i < n) do
begin
insert into TEST_TABLE (VALUE_1, VALUE_2, VALUE_3)
values (:i, :i, :i);
i = i + 1;
end
end

^

SET TERM ; ^
COMMIT;

Results (memory and commit stats is omittted)

1. Using Firebird 2.5.6.27018

execute procedure MAKE_UPDATES;
Elapsed time= 0.99 sec
Buffers = 2048
Reads = 42
Writes 975
Fetches = 1054141
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.19 sec
Buffers = 2048
Reads = 0
Writes 984
Fetches = 1304860
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.84 sec
Buffers = 2048
Reads = 0
Writes 749
Fetches = 2218769
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.86 sec
Buffers = 2048
Reads = 0
Writes 761
Fetches = 2139364
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.61 sec
Buffers = 2048
Reads = 0
Writes 766
Fetches = 2113376
commit;

2. Using Firebird 3.0.1.32547

execute procedure MAKE_UPDATES;
Elapsed time= 2.218 sec
Buffers = 2048
Reads = 32
Writes = 975
Fetches = 1053352
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 2.672 sec
Buffers = 2048
Reads = 0
Writes = 984
Fetches = 1304191
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 2.958 sec
Buffers = 2048
Reads = 0
Writes = 1050
Fetches = 2503752
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 3.069 sec
Buffers = 2048
Reads = 0
Writes = 1393
Fetches = 2502999
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 2.928 sec
Buffers = 2048
Reads = 0
Writes = 1057
Fetches = 2502628
commit;

Commented by: @hvlad

The regression was introduced with a fix for CORE4914

Commented by: @hvlad

Stats on Firebird 4.0.0.288 with patch

execute procedure MAKE_UPDATES;
Elapsed time= 1.005 sec
Buffers = 2048
Reads = 28
Writes = 975
Fetches = 1053362
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.315 sec
Buffers = 2048
Reads = 0
Writes = 1236
Fetches = 1304551
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.389 sec
Buffers = 2048
Reads = 0
Writes = 1165
Fetches = 2502620
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.468 sec
Buffers = 2048
Reads = 0
Writes = 1527
Fetches = 2502337
commit;

execute procedure MAKE_UPDATES;
Elapsed time= 1.349 sec
Buffers = 2048
Reads = 0
Writes = 1165
Fetches = 2501646
commit;

Commented by: @pavel-zotov

Trace logs with config:

log_transactions = true
log_statement_finish = true

-- show following (bigger values - for EXECUTE PROCEDURE, smaller - for COMMIT):

WI-V2.5.6.27023

4019 ms, 8 read(s), 2571 write(s), 1057721 fetch(es), 356280 mark(s)
35 ms, 1 read(s), 140 write(s), 1 fetch(es), 1 mark(s)
6880 ms, 1392 read(s), 5079 write(s), 1357467 fetch(es), 407681 mark(s)
118 ms, 1 read(s), 236 write(s), 1 fetch(es), 1 mark(s)
7975 ms, 4464 read(s), 4934 write(s), 2612922 fetch(es), 806453 mark(s)
68 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
8104 ms, 4458 read(s), 4922 write(s), 2611471 fetch(es), 806423 mark(s)
89 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
7723 ms, 4465 read(s), 4928 write(s), 2611434 fetch(es), 806426 mark(s)
33 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
8211 ms, 4459 read(s), 4922 write(s), 2611429 fetch(es), 806420 mark(s)
43 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
7782 ms, 4466 read(s), 4928 write(s), 2611434 fetch(es), 806423 mark(s)
107 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
8139 ms, 4460 read(s), 4922 write(s), 2611429 fetch(es), 806417 mark(s)
75 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
7826 ms, 4466 read(s), 4927 write(s), 2611434 fetch(es), 806420 mark(s)
102 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
8156 ms, 4458 read(s), 4930 write(s), 2611456 fetch(es), 806441 mark(s)
61 ms, 1 read(s), 252 write(s), 1 fetch(es), 1 mark(s)
8004 ms, 4465 read(s), 4925 write(s), 2611434 fetch(es), 806417 mark(s)
140 ms, 1 read(s), 249 write(s), 1 fetch(es), 1 mark(s)
9010 ms, 4459 read(s), 4930 write(s), 2611459 fetch(es), 806438 mark(s)
42 ms, 1 read(s), 252 write(s), 1 fetch(es), 1 mark(s)

WI-V3.0.1.32566

11431 ms, 8 read(s), 975 write(s), 1053183 fetch(es), 352462 mark(s)
138 ms, 375 write(s), 1 fetch(es), 1 mark(s)
12895 ms, 984 write(s), 1304191 fetch(es), 402770 mark(s)
716 ms, 1379 write(s), 1 fetch(es), 1 mark(s)
15829 ms, 9 write(s), 1905526 fetch(es), 602321 mark(s)
681 ms, 1372 write(s), 1 fetch(es), 1 mark(s)
16018 ms, 121 write(s), 1839431 fetch(es), 580376 mark(s)
524 ms, 1002 write(s), 1 fetch(es), 1 mark(s)
15583 ms, 1899236 fetch(es), 600279 mark(s)
690 ms, 1346 write(s), 1 fetch(es), 1 mark(s)
15914 ms, 7 write(s), 1838875 fetch(es), 580188 mark(s)
594 ms, 996 write(s), 1 fetch(es), 1 mark(s)
15588 ms, 1891369 fetch(es), 597695 mark(s)
694 ms, 1325 write(s), 1 fetch(es), 1 mark(s)
15891 ms, 10 write(s), 1838932 fetch(es), 580196 mark(s)
506 ms, 997 write(s), 1 fetch(es), 1 mark(s)
15775 ms, 1887593 fetch(es), 596416 mark(s)
764 ms, 1296 write(s), 1 fetch(es), 1 mark(s)
15847 ms, 9 write(s), 1835952 fetch(es), 579207 mark(s)
500 ms, 998 write(s), 1 fetch(es), 1 mark(s)
15616 ms, 1883895 fetch(es), 595176 mark(s)
637 ms, 1267 write(s), 1 fetch(es), 1 mark(s)

WI-T4.0.0.312

5120 ms, 8 read(s), 975 write(s), 1053183 fetch(es), 352462 mark(s)
171 ms, 375 write(s), 1 fetch(es), 1 mark(s)
6372 ms, 1236 write(s), 1304527 fetch(es), 403106 mark(s)
752 ms, 1379 write(s), 1 fetch(es), 1 mark(s)
9075 ms, 7 write(s), 1910488 fetch(es), 603967 mark(s)
735 ms, 1442 write(s), 1 fetch(es), 1 mark(s)
9687 ms, 298 write(s), 1836660 fetch(es), 579447 mark(s)
563 ms, 1058 write(s), 1 fetch(es), 1 mark(s)
8772 ms, 18 write(s), 1897749 fetch(es), 599813 mark(s)
733 ms, 1412 write(s), 1 fetch(es), 1 mark(s)
9486 ms, 236 write(s), 1836932 fetch(es), 579544 mark(s)
555 ms, 1050 write(s), 1 fetch(es), 1 mark(s)
8767 ms, 9 write(s), 1892261 fetch(es), 597985 mark(s)
699 ms, 1387 write(s), 1 fetch(es), 1 mark(s)
9346 ms, 168 write(s), 1837526 fetch(es), 579733 mark(s)
552 ms, 1043 write(s), 1 fetch(es), 1 mark(s)
8794 ms, 1887371 fetch(es), 596344 mark(s)
753 ms, 1355 write(s), 1 fetch(es), 1 mark(s)
9194 ms, 51 write(s), 1834030 fetch(es), 578571 mark(s)
549 ms, 1045 write(s), 1 fetch(es), 1 mark(s)
8791 ms, 9 write(s), 1882791 fetch(es), 594825 mark(s)
757 ms, 1324 write(s), 1 fetch(es), 1 mark(s)

Every database was created with FW = ON,page_size = default.
Machine: CPU 3.0 GHz, 2core,ram 2 Gb.

DefaultDbCachePages = 256 on 2.5 and default on 3.0 & 4.0.
Packed logs see in attached .7z