XRANGE and XREVRANGE in Redis - Step-by-Step Execution

Concept Flow - XRANGE and XREVRANGE

Start with Stream Key

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Specify Start and End IDs

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Choose XRANGE or XREVRANGE

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Fetch Entries in Range

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Return Entries in Order

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End

XRANGE and XREVRANGE fetch entries from a Redis stream between two IDs, returning them in forward or reverse order.

Execution Sample

Redis

XRANGE mystream 1609459200000-0 1609459205000-0
XREVRANGE mystream 1609459205000-0 1609459200000-0

Fetch entries from 'mystream' between two timestamps, forward with XRANGE and reverse with XREVRANGE.

Execution Table

Step	Command	Start ID	End ID	Order	Entries Returned
1	XRANGE mystream 1609459200000-0 1609459205000-0	1609459200000-0	1609459205000-0	Forward	[{id:"1609459200000-0", fields:{a:1}}, {id:"1609459201000-0", fields:{b:2}}, {id:"1609459203000-0", fields:{c:3}}]
2	XREVRANGE mystream 1609459205000-0 1609459200000-0	1609459205000-0	1609459200000-0	Reverse	[{id:"1609459203000-0", fields:{c:3}}, {id:"1609459201000-0", fields:{b:2}}, {id:"1609459200000-0", fields:{a:1}}]
3	XRANGE mystream 1609459204000-0 1609459205000-0	1609459204000-0	1609459205000-0	Forward	[]
4	XREVRANGE mystream 1609459200000-0 1609459200000-0	1609459200000-0	1609459200000-0	Reverse	[{id:"1609459200000-0", fields:{a:1}}]
5	XRANGE mystream - +	-	+	Forward	[All entries from oldest to newest]
6	XREVRANGE mystream + -	+	-	Reverse	[All entries from newest to oldest]
7	Exit	-	-	-	No more entries or invalid range

💡 Execution stops when no entries match the range or the range is invalid.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
Start ID	1609459200000-0	1609459200000-0	1609459205000-0	1609459204000-0	1609459200000-0	-
End ID	1609459205000-0	1609459205000-0	1609459200000-0	1609459205000-0	1609459200000-0	-
Order	Forward	Forward	Reverse	Forward	Reverse	-
Entries Returned	[]	[3 entries]	[3 entries]	[]	[1 entry]	-

Key Moments - 3 Insights

Why does XRANGE return entries in ascending order but XREVRANGE returns them in descending order?

Because XRANGE reads from the start ID to the end ID in forward time order (see execution_table rows 1 and 2), while XREVRANGE reads backwards from the end ID to the start ID.

What happens if the start ID is greater than the end ID in XRANGE?

XRANGE will return an empty list because the range is invalid or no entries fall in that range (see execution_table row 3).

How do the special IDs '+' and '-' affect the range?

'+' means the maximum possible ID (newest), '-' means the minimum possible ID (oldest). Using them fetches all entries from oldest to newest or newest to oldest (see execution_table rows 5 and 6).

Visual Quiz - 3 Questions

Look at the execution_table row 1, what is the order of entries returned by XRANGE?

A Descending (newest to oldest)

B Ascending (oldest to newest)

C Random order

D No entries returned

💡 Hint

Check the 'Order' column in row 1 of execution_table.

At which step does XRANGE return an empty list due to no entries in range?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Entries Returned' column for empty lists in execution_table.

If you swap the start and end IDs in XREVRANGE, how does the entries order change?

A It stays the same

B It reverses to ascending order

C It returns no entries

D It causes an error

💡 Hint

Refer to execution_table row 3 and the explanation about invalid ranges.

Concept Snapshot

XRANGE key start end [COUNT n]
XREVRANGE key end start [COUNT n]

- XRANGE returns stream entries from start to end ID in ascending order.
- XREVRANGE returns entries from end to start ID in descending order.
- Use '-' for earliest ID and '+' for latest ID.
- If no entries match, returns empty list.

Full Transcript

XRANGE and XREVRANGE are Redis commands to read entries from a stream between two IDs. XRANGE reads forward from the start ID to the end ID, returning entries in ascending order. XREVRANGE reads backward from the end ID to the start ID, returning entries in descending order. Special IDs '-' and '+' represent the earliest and latest entries respectively. If the range is invalid or no entries exist in the range, the commands return an empty list. This visual execution shows step-by-step how these commands fetch entries and how the order and range affect the results.