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create tmp schema to reference when creating partitioned table

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* if we use the actual old job events table
  and make tweaks to its schema
  namely, dropping the pkey constraint,
  then when we go to migrate the old job events
  we will be forcing postgres to do a sequential scan
  on the old table, which effectively causes the migration to hang
This commit is contained in:
Jim Ladd 2021-03-08 14:00:57 -08:00
parent 28f9c0be0b
commit 0fa0a517ac
1 changed files with 14 additions and 3 deletions
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17
awx/main/migrations/0130_event_partitions.py
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@ -37,21 +37,32 @@ def migrate_event_data(apps, schema_editor):
f'ALTER TABLE {tblname} RENAME TO _unpartitioned_{tblname}'
)
# create a copy of the table that we will use as a reference for schema
# otherwise, the schema changes we would make on the old jobevents table
# (namely, dropping the primary key constraint) would cause the migration
# to suffer a serious performance degradation
cursor.execute(
f'CREATE TABLE tmp_{tblname} '
f'(LIKE _unpartitioned_{tblname} INCLUDING ALL)'
)
# drop primary key constraint; in a partioned table
# constraints must include the partition key itself
# TODO: do more generic search for pkey constraints
# instead of hardcoding this one that applies to main_jobevent
cursor.execute(
f'ALTER TABLE _unpartitioned_{tblname} DROP CONSTRAINT {tblname}_pkey1'
f'ALTER TABLE tmp_{tblname} DROP CONSTRAINT {tblname}_pkey1'
)
# create parent table
cursor.execute(
f'CREATE TABLE {tblname} '
f'(LIKE _unpartitioned_{tblname} INCLUDING ALL, job_created TIMESTAMP WITH TIME ZONE NOT NULL) '
f'(LIKE tmp_{tblname} INCLUDING ALL, job_created TIMESTAMP WITH TIME ZONE NOT NULL) '
f'PARTITION BY RANGE(job_created);'
)
cursor.execute(f'DROP TABLE tmp_{tblname}')
# let's go ahead and add and subtract a few indexes while we're here
cursor.execute(f'CREATE INDEX {tblname}_modified_idx ON {tblname} (modified);')
cursor.execute(f'DROP INDEX IF EXISTS {tblname}_job_id_brin_idx;')
@ -64,7 +75,7 @@ def migrate_event_data(apps, schema_editor):
current_time = now()
# .. as well as initial partition containing all existing events
# create initial partition containing all existing events
epoch = datetime.utcfromtimestamp(0)
create_partition(tblname, epoch, current_time, 'old_events')